Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

39 files changed, 6003 insertions, 0 deletions

diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
new file mode 100644
index 000000000..1c2d4b29a
--- /dev/null
+++ b/arch/um/kernel/Makefile
@@ -0,0 +1,65 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux,intel}.com)
+#
+
+# Don't instrument UML-specific code; without this, we may crash when
+# accessing the instrumentation buffer for the first time from the
+# kernel.
+KCOV_INSTRUMENT                := n
+
+CPPFLAGS_vmlinux.lds := -DSTART=$(LDS_START)		\
+                        -DELF_ARCH=$(LDS_ELF_ARCH)	\
+                        -DELF_FORMAT=$(LDS_ELF_FORMAT)	\
+			$(LDS_EXTRA)
+extra-y := vmlinux.lds
+
+obj-y = config.o exec.o exitcode.o irq.o ksyms.o mem.o \
+	physmem.o process.o ptrace.o reboot.o sigio.o \
+	signal.o sysrq.o time.o tlb.o trap.o \
+	um_arch.o umid.o maccess.o kmsg_dump.o capflags.o skas/
+obj-y += load_file.o
+
+obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o
+obj-$(CONFIG_GPROF)	+= gprof_syms.o
+obj-$(CONFIG_OF) += dtb.o
+obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
+obj-$(CONFIG_STACKTRACE) += stacktrace.o
+obj-$(CONFIG_GENERIC_PCI_IOMAP) += ioport.o
+
+USER_OBJS := config.o
+
+include arch/um/scripts/Makefile.rules
+
+targets := config.c config.tmp capflags.c
+
+# Be careful with the below Sed code - sed is pitfall-rich!
+# We use sed to lower build requirements, for "embedded" builders for instance.
+
+$(obj)/config.tmp: $(objtree)/.config FORCE
+	$(call if_changed,quote1)
+
+quiet_cmd_quote1 = QUOTE   $@
+      cmd_quote1 = sed -e 's/"/\\"/g' -e 's/^/"/' -e 's/$$/\\n",/' \
+		   $< > $@
+
+$(obj)/config.c: $(src)/config.c.in $(obj)/config.tmp FORCE
+	$(call if_changed,quote2)
+
+quiet_cmd_mkcapflags = MKCAP   $@
+      cmd_mkcapflags = $(CONFIG_SHELL) $(srctree)/$(src)/../../x86/kernel/cpu/mkcapflags.sh $@ $^
+
+cpufeature = $(src)/../../x86/include/asm/cpufeatures.h
+vmxfeature = $(src)/../../x86/include/asm/vmxfeatures.h
+
+$(obj)/capflags.c: $(cpufeature) $(vmxfeature) $(src)/../../x86/kernel/cpu/mkcapflags.sh FORCE
+	$(call if_changed,mkcapflags)
+
+quiet_cmd_quote2 = QUOTE   $@
+      cmd_quote2 = sed -e '/CONFIG/{'          \
+		  -e 's/"CONFIG"//'            \
+		  -e 'r $(obj)/config.tmp'     \
+		  -e 'a \'                     \
+		  -e '""'                      \
+		  -e '}'                       \
+		  $< > $@
diff --git a/arch/um/kernel/asm-offsets.c b/arch/um/kernel/asm-offsets.c
new file mode 100644
index 000000000..1fb12235a
--- /dev/null
+++ b/arch/um/kernel/asm-offsets.c
@@ -0,0 +1 @@
+#include <sysdep/kernel-offsets.h>
diff --git a/arch/um/kernel/config.c.in b/arch/um/kernel/config.c.in
new file mode 100644
index 000000000..3ece3c3b3
--- /dev/null
+++ b/arch/um/kernel/config.c.in
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <init.h>
+
+static __initdata const char *config[] = {
+"CONFIG"
+};
+
+static int __init print_config(char *line, int *add)
+{
+	int i;
+	for (i = 0; i < sizeof(config)/sizeof(config[0]); i++)
+		printf("%s", config[i]);
+	exit(0);
+}
+
+__uml_setup("--showconfig", print_config,
+"--showconfig\n"
+"    Prints the config file that this UML binary was generated from.\n\n"
+);
+
diff --git a/arch/um/kernel/dtb.c b/arch/um/kernel/dtb.c
new file mode 100644
index 000000000..484141b06
--- /dev/null
+++ b/arch/um/kernel/dtb.c
@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/init.h>
+#include <linux/of_fdt.h>
+#include <linux/printk.h>
+#include <linux/memblock.h>
+#include <init.h>
+
+#include "um_arch.h"
+
+static char *dtb __initdata;
+
+void uml_dtb_init(void)
+{
+	long long size;
+	void *area;
+
+	area = uml_load_file(dtb, &size);
+	if (!area)
+		return;
+
+	if (!early_init_dt_scan(area)) {
+		pr_err("invalid DTB %s\n", dtb);
+		memblock_free(area, size);
+		return;
+	}
+
+	early_init_fdt_scan_reserved_mem();
+	unflatten_device_tree();
+}
+
+static int __init uml_dtb_setup(char *line, int *add)
+{
+	dtb = line;
+	return 0;
+}
+
+__uml_setup("dtb=", uml_dtb_setup,
+"dtb=<file>\n"
+"    Boot the kernel with the devicetree blob from the specified file.\n"
+);
diff --git a/arch/um/kernel/dyn.lds.S b/arch/um/kernel/dyn.lds.S
new file mode 100644
index 000000000..2b7fc5b54
--- /dev/null
+++ b/arch/um/kernel/dyn.lds.S
@@ -0,0 +1,181 @@
+#include <asm/vmlinux.lds.h>
+#include <asm/page.h>
+
+OUTPUT_FORMAT(ELF_FORMAT)
+OUTPUT_ARCH(ELF_ARCH)
+ENTRY(_start)
+jiffies = jiffies_64;
+
+VERSION {
+  {
+    local: *;
+  };
+}
+
+SECTIONS
+{
+  PROVIDE (__executable_start = START);
+  . = START + SIZEOF_HEADERS;
+  .interp         : { *(.interp) }
+  __binary_start = .;
+  . = ALIGN(4096);		/* Init code and data */
+  _text = .;
+  INIT_TEXT_SECTION(PAGE_SIZE)
+
+  . = ALIGN(PAGE_SIZE);
+
+  /* Read-only sections, merged into text segment: */
+  .hash           : { *(.hash) }
+  .gnu.hash       : { *(.gnu.hash) }
+  .dynsym         : { *(.dynsym) }
+  .dynstr         : { *(.dynstr) }
+  .gnu.version    : { *(.gnu.version) }
+  .gnu.version_d  : { *(.gnu.version_d) }
+  .gnu.version_r  : { *(.gnu.version_r) }
+  .rel.init       : { *(.rel.init) }
+  .rela.init      : { *(.rela.init) }
+  .rel.text       : { *(.rel.text .rel.text.* .rel.gnu.linkonce.t.*) }
+  .rela.text      : { *(.rela.text .rela.text.* .rela.gnu.linkonce.t.*) }
+  .rel.fini       : { *(.rel.fini) }
+  .rela.fini      : { *(.rela.fini) }
+  .rel.rodata     : { *(.rel.rodata .rel.rodata.* .rel.gnu.linkonce.r.*) }
+  .rela.rodata    : { *(.rela.rodata .rela.rodata.* .rela.gnu.linkonce.r.*) }
+  .rel.data       : { *(.rel.data .rel.data.* .rel.gnu.linkonce.d.*) }
+  .rela.data      : { *(.rela.data .rela.data.* .rela.gnu.linkonce.d.*) }
+  .rel.tdata	  : { *(.rel.tdata .rel.tdata.* .rel.gnu.linkonce.td.*) }
+  .rela.tdata	  : { *(.rela.tdata .rela.tdata.* .rela.gnu.linkonce.td.*) }
+  .rel.tbss	  : { *(.rel.tbss .rel.tbss.* .rel.gnu.linkonce.tb.*) }
+  .rela.tbss	  : { *(.rela.tbss .rela.tbss.* .rela.gnu.linkonce.tb.*) }
+  .rel.ctors      : { *(.rel.ctors) }
+  .rela.ctors     : { *(.rela.ctors) }
+  .rel.dtors      : { *(.rel.dtors) }
+  .rela.dtors     : { *(.rela.dtors) }
+  .rel.got        : { *(.rel.got) }
+  .rela.got       : { *(.rela.got) }
+  .rel.bss        : { *(.rel.bss .rel.bss.* .rel.gnu.linkonce.b.*) }
+  .rela.bss       : { *(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*) }
+  .rel.plt : {
+	*(.rel.plt)
+	PROVIDE_HIDDEN(__rel_iplt_start = .);
+	*(.rel.iplt)
+	PROVIDE_HIDDEN(__rel_iplt_end = .);
+  }
+  .rela.plt : {
+	*(.rela.plt)
+	PROVIDE_HIDDEN(__rela_iplt_start = .);
+	*(.rela.iplt)
+	PROVIDE_HIDDEN(__rela_iplt_end = .);
+  }
+  .init           : {
+    KEEP (*(.init))
+  } =0x90909090
+  .plt            : { *(.plt) }
+  .text           : {
+    _stext = .;
+    TEXT_TEXT
+    SCHED_TEXT
+    CPUIDLE_TEXT
+    LOCK_TEXT
+    IRQENTRY_TEXT
+    SOFTIRQENTRY_TEXT
+    *(.fixup)
+    *(.stub .text.* .gnu.linkonce.t.*)
+    /* .gnu.warning sections are handled specially by elf32.em.  */
+    *(.gnu.warning)
+
+    . = ALIGN(PAGE_SIZE);
+  } =0x90909090
+  . = ALIGN(PAGE_SIZE);
+  .syscall_stub : {
+	__syscall_stub_start = .;
+	*(.__syscall_stub*)
+	__syscall_stub_end = .;
+  }
+  .fini           : {
+    KEEP (*(.fini))
+  } =0x90909090
+
+  .kstrtab : { *(.kstrtab) }
+
+  #include <asm/common.lds.S>
+
+  __init_begin = .;
+  init.data : { INIT_DATA }
+  __init_end = .;
+
+  /* Ensure the __preinit_array_start label is properly aligned.  We
+     could instead move the label definition inside the section, but
+     the linker would then create the section even if it turns out to
+     be empty, which isn't pretty.  */
+  . = ALIGN(32 / 8);
+  .preinit_array     : { *(.preinit_array) }
+  .init_array     : {
+    *(.kasan_init)
+    *(.init_array.*)
+    *(.init_array)
+  }
+  .fini_array     : { *(.fini_array) }
+  .data           : {
+    INIT_TASK_DATA(KERNEL_STACK_SIZE)
+    . = ALIGN(KERNEL_STACK_SIZE);
+    *(.data..init_irqstack)
+    DATA_DATA
+    *(.data.* .gnu.linkonce.d.*)
+    SORT(CONSTRUCTORS)
+  }
+  .data1          : { *(.data1) }
+  .tdata	  : { *(.tdata .tdata.* .gnu.linkonce.td.*) }
+  .tbss		  : { *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon) }
+  .eh_frame       : { KEEP (*(.eh_frame)) }
+  .gcc_except_table   : { *(.gcc_except_table) }
+  .dynamic        : { *(.dynamic) }
+  .ctors          : {
+    /* gcc uses crtbegin.o to find the start of
+       the constructors, so we make sure it is
+       first.  Because this is a wildcard, it
+       doesn't matter if the user does not
+       actually link against crtbegin.o; the
+       linker won't look for a file to match a
+       wildcard.  The wildcard also means that it
+       doesn't matter which directory crtbegin.o
+       is in.  */
+    KEEP (*crtbegin.o(.ctors))
+    /* We don't want to include the .ctor section from
+       from the crtend.o file until after the sorted ctors.
+       The .ctor section from the crtend file contains the
+       end of ctors marker and it must be last */
+    KEEP (*(EXCLUDE_FILE (*crtend.o ) .ctors))
+    KEEP (*(SORT(.ctors.*)))
+    KEEP (*(.ctors))
+  }
+  .dtors          : {
+    KEEP (*crtbegin.o(.dtors))
+    KEEP (*(EXCLUDE_FILE (*crtend.o ) .dtors))
+    KEEP (*(SORT(.dtors.*)))
+    KEEP (*(.dtors))
+  }
+  .jcr            : { KEEP (*(.jcr)) }
+  .got            : { *(.got.plt) *(.got) }
+  _edata = .;
+  PROVIDE (edata = .);
+  .bss            : {
+   __bss_start = .;
+   *(.dynbss)
+   *(.bss .bss.* .gnu.linkonce.b.*)
+   *(COMMON)
+   /* Align here to ensure that the .bss section occupies space up to
+      _end.  Align after .bss to ensure correct alignment even if the
+      .bss section disappears because there are no input sections.  */
+   . = ALIGN(32 / 8);
+  . = ALIGN(32 / 8);
+  }
+   __bss_stop = .;
+  _end = .;
+  PROVIDE (end = .);
+
+  STABS_DEBUG
+  DWARF_DEBUG
+  ELF_DETAILS
+
+  DISCARDS
+}
diff --git a/arch/um/kernel/early_printk.c b/arch/um/kernel/early_printk.c
new file mode 100644
index 000000000..c350c2331
--- /dev/null
+++ b/arch/um/kernel/early_printk.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2011 Richard Weinberger <richrd@nod.at>
+ */
+
+#include <linux/kernel.h>
+#include <linux/console.h>
+#include <linux/init.h>
+#include <os.h>
+
+static void early_console_write(struct console *con, const char *s, unsigned int n)
+{
+	um_early_printk(s, n);
+}
+
+static struct console early_console_dev = {
+	.name = "earlycon",
+	.write = early_console_write,
+	.flags = CON_BOOT,
+	.index = -1,
+};
+
+static int __init setup_early_printk(char *buf)
+{
+	if (!early_console) {
+		early_console = &early_console_dev;
+		register_console(&early_console_dev);
+	}
+	return 0;
+}
+
+early_param("earlyprintk", setup_early_printk);
diff --git a/arch/um/kernel/exec.c b/arch/um/kernel/exec.c
new file mode 100644
index 000000000..58938d758
--- /dev/null
+++ b/arch/um/kernel/exec.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/stddef.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/ptrace.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/task.h>
+#include <linux/sched/task_stack.h>
+#include <linux/slab.h>
+#include <asm/current.h>
+#include <asm/processor.h>
+#include <linux/uaccess.h>
+#include <as-layout.h>
+#include <mem_user.h>
+#include <registers.h>
+#include <skas.h>
+#include <os.h>
+
+void flush_thread(void)
+{
+	void *data = NULL;
+	int ret;
+
+	arch_flush_thread(&current->thread.arch);
+
+	ret = unmap(&current->mm->context.id, 0, TASK_SIZE, 1, &data);
+	if (ret) {
+		printk(KERN_ERR "flush_thread - clearing address space failed, "
+		       "err = %d\n", ret);
+		force_sig(SIGKILL);
+	}
+	get_safe_registers(current_pt_regs()->regs.gp,
+			   current_pt_regs()->regs.fp);
+
+	__switch_mm(&current->mm->context.id);
+}
+
+void start_thread(struct pt_regs *regs, unsigned long eip, unsigned long esp)
+{
+	PT_REGS_IP(regs) = eip;
+	PT_REGS_SP(regs) = esp;
+	clear_thread_flag(TIF_SINGLESTEP);
+#ifdef SUBARCH_EXECVE1
+	SUBARCH_EXECVE1(regs->regs);
+#endif
+}
+EXPORT_SYMBOL(start_thread);
diff --git a/arch/um/kernel/exitcode.c b/arch/um/kernel/exitcode.c
new file mode 100644
index 000000000..43edc2aa5
--- /dev/null
+++ b/arch/um/kernel/exitcode.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/ctype.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+
+/*
+ * If read and write race, the read will still atomically read a valid
+ * value.
+ */
+int uml_exitcode = 0;
+
+static int exitcode_proc_show(struct seq_file *m, void *v)
+{
+	int val;
+
+	/*
+	 * Save uml_exitcode in a local so that we don't need to guarantee
+	 * that sprintf accesses it atomically.
+	 */
+	val = uml_exitcode;
+	seq_printf(m, "%d\n", val);
+	return 0;
+}
+
+static int exitcode_proc_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, exitcode_proc_show, NULL);
+}
+
+static ssize_t exitcode_proc_write(struct file *file,
+		const char __user *buffer, size_t count, loff_t *pos)
+{
+	char *end, buf[sizeof("nnnnn\0")];
+	size_t size;
+	int tmp;
+
+	size = min(count, sizeof(buf));
+	if (copy_from_user(buf, buffer, size))
+		return -EFAULT;
+
+	tmp = simple_strtol(buf, &end, 0);
+	if ((*end != '\0') && !isspace(*end))
+		return -EINVAL;
+
+	uml_exitcode = tmp;
+	return count;
+}
+
+static const struct proc_ops exitcode_proc_ops = {
+	.proc_open	= exitcode_proc_open,
+	.proc_read	= seq_read,
+	.proc_lseek	= seq_lseek,
+	.proc_release	= single_release,
+	.proc_write	= exitcode_proc_write,
+};
+
+static int make_proc_exitcode(void)
+{
+	struct proc_dir_entry *ent;
+
+	ent = proc_create("exitcode", 0600, NULL, &exitcode_proc_ops);
+	if (ent == NULL) {
+		printk(KERN_WARNING "make_proc_exitcode : Failed to register "
+		       "/proc/exitcode\n");
+		return 0;
+	}
+	return 0;
+}
+
+__initcall(make_proc_exitcode);
diff --git a/arch/um/kernel/gprof_syms.c b/arch/um/kernel/gprof_syms.c
new file mode 100644
index 000000000..84d536908
--- /dev/null
+++ b/arch/um/kernel/gprof_syms.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+/* 
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/module.h>
+
+extern void mcount(void);
+EXPORT_SYMBOL(mcount);
diff --git a/arch/um/kernel/initrd.c b/arch/um/kernel/initrd.c
new file mode 100644
index 000000000..47b8cb1a1
--- /dev/null
+++ b/arch/um/kernel/initrd.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/init.h>
+#include <linux/memblock.h>
+#include <linux/initrd.h>
+#include <asm/types.h>
+#include <init.h>
+#include <os.h>
+
+#include "um_arch.h"
+
+/* Changed by uml_initrd_setup, which is a setup */
+static char *initrd __initdata = NULL;
+
+int __init read_initrd(void)
+{
+	unsigned long long size;
+	void *area;
+
+	if (!initrd)
+		return 0;
+
+	area = uml_load_file(initrd, &size);
+	if (!area)
+		return 0;
+
+	initrd_start = (unsigned long) area;
+	initrd_end = initrd_start + size;
+	return 0;
+}
+
+static int __init uml_initrd_setup(char *line, int *add)
+{
+	initrd = line;
+	return 0;
+}
+
+__uml_setup("initrd=", uml_initrd_setup,
+"initrd=<initrd image>\n"
+"    This is used to boot UML from an initrd image.  The argument is the\n"
+"    name of the file containing the image.\n\n"
+);
diff --git a/arch/um/kernel/ioport.c b/arch/um/kernel/ioport.c
new file mode 100644
index 000000000..7220615b3
--- /dev/null
+++ b/arch/um/kernel/ioport.c
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021 Intel Corporation
+ * Author: Johannes Berg <johannes@sipsolutions.net>
+ */
+#include <asm/iomap.h>
+#include <asm-generic/pci_iomap.h>
+
+void __iomem *__pci_ioport_map(struct pci_dev *dev, unsigned long port,
+			       unsigned int nr)
+{
+	return NULL;
+}
diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c
new file mode 100644
index 000000000..a8873d9bc
--- /dev/null
+++ b/arch/um/kernel/irq.c
@@ -0,0 +1,768 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2017 - Cambridge Greys Ltd
+ * Copyright (C) 2011 - 2014 Cisco Systems Inc
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Derived (i.e. mostly copied) from arch/i386/kernel/irq.c:
+ *	Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
+ */
+
+#include <linux/cpumask.h>
+#include <linux/hardirq.h>
+#include <linux/interrupt.h>
+#include <linux/kernel_stat.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <as-layout.h>
+#include <kern_util.h>
+#include <os.h>
+#include <irq_user.h>
+#include <irq_kern.h>
+#include <linux/time-internal.h>
+
+
+extern void free_irqs(void);
+
+/* When epoll triggers we do not know why it did so
+ * we can also have different IRQs for read and write.
+ * This is why we keep a small irq_reg array for each fd -
+ * one entry per IRQ type
+ */
+struct irq_reg {
+	void *id;
+	int irq;
+	/* it's cheaper to store this than to query it */
+	int events;
+	bool active;
+	bool pending;
+	bool wakeup;
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+	bool pending_on_resume;
+	void (*timetravel_handler)(int, int, void *,
+				   struct time_travel_event *);
+	struct time_travel_event event;
+#endif
+};
+
+struct irq_entry {
+	struct list_head list;
+	int fd;
+	struct irq_reg reg[NUM_IRQ_TYPES];
+	bool suspended;
+	bool sigio_workaround;
+};
+
+static DEFINE_SPINLOCK(irq_lock);
+static LIST_HEAD(active_fds);
+static DECLARE_BITMAP(irqs_allocated, UM_LAST_SIGNAL_IRQ);
+static bool irqs_suspended;
+
+static void irq_io_loop(struct irq_reg *irq, struct uml_pt_regs *regs)
+{
+/*
+ * irq->active guards against reentry
+ * irq->pending accumulates pending requests
+ * if pending is raised the irq_handler is re-run
+ * until pending is cleared
+ */
+	if (irq->active) {
+		irq->active = false;
+
+		do {
+			irq->pending = false;
+			do_IRQ(irq->irq, regs);
+		} while (irq->pending);
+
+		irq->active = true;
+	} else {
+		irq->pending = true;
+	}
+}
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+static void irq_event_handler(struct time_travel_event *ev)
+{
+	struct irq_reg *reg = container_of(ev, struct irq_reg, event);
+
+	/* do nothing if suspended - just to cause a wakeup */
+	if (irqs_suspended)
+		return;
+
+	generic_handle_irq(reg->irq);
+}
+
+static bool irq_do_timetravel_handler(struct irq_entry *entry,
+				      enum um_irq_type t)
+{
+	struct irq_reg *reg = &entry->reg[t];
+
+	if (!reg->timetravel_handler)
+		return false;
+
+	/*
+	 * Handle all messages - we might get multiple even while
+	 * interrupts are already suspended, due to suspend order
+	 * etc. Note that time_travel_add_irq_event() will not add
+	 * an event twice, if it's pending already "first wins".
+	 */
+	reg->timetravel_handler(reg->irq, entry->fd, reg->id, &reg->event);
+
+	if (!reg->event.pending)
+		return false;
+
+	if (irqs_suspended)
+		reg->pending_on_resume = true;
+	return true;
+}
+#else
+static bool irq_do_timetravel_handler(struct irq_entry *entry,
+				      enum um_irq_type t)
+{
+	return false;
+}
+#endif
+
+static void sigio_reg_handler(int idx, struct irq_entry *entry, enum um_irq_type t,
+			      struct uml_pt_regs *regs,
+			      bool timetravel_handlers_only)
+{
+	struct irq_reg *reg = &entry->reg[t];
+
+	if (!reg->events)
+		return;
+
+	if (os_epoll_triggered(idx, reg->events) <= 0)
+		return;
+
+	if (irq_do_timetravel_handler(entry, t))
+		return;
+
+	/*
+	 * If we're called to only run time-travel handlers then don't
+	 * actually proceed but mark sigio as pending (if applicable).
+	 * For suspend/resume, timetravel_handlers_only may be true
+	 * despite time-travel not being configured and used.
+	 */
+	if (timetravel_handlers_only) {
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+		mark_sigio_pending();
+#endif
+		return;
+	}
+
+	irq_io_loop(reg, regs);
+}
+
+static void _sigio_handler(struct uml_pt_regs *regs,
+			   bool timetravel_handlers_only)
+{
+	struct irq_entry *irq_entry;
+	int n, i;
+
+	if (timetravel_handlers_only && !um_irq_timetravel_handler_used())
+		return;
+
+	while (1) {
+		/* This is now lockless - epoll keeps back-referencesto the irqs
+		 * which have trigger it so there is no need to walk the irq
+		 * list and lock it every time. We avoid locking by turning off
+		 * IO for a specific fd by executing os_del_epoll_fd(fd) before
+		 * we do any changes to the actual data structures
+		 */
+		n = os_waiting_for_events_epoll();
+
+		if (n <= 0) {
+			if (n == -EINTR)
+				continue;
+			else
+				break;
+		}
+
+		for (i = 0; i < n ; i++) {
+			enum um_irq_type t;
+
+			irq_entry = os_epoll_get_data_pointer(i);
+
+			for (t = 0; t < NUM_IRQ_TYPES; t++)
+				sigio_reg_handler(i, irq_entry, t, regs,
+						  timetravel_handlers_only);
+		}
+	}
+
+	if (!timetravel_handlers_only)
+		free_irqs();
+}
+
+void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
+{
+	_sigio_handler(regs, irqs_suspended);
+}
+
+static struct irq_entry *get_irq_entry_by_fd(int fd)
+{
+	struct irq_entry *walk;
+
+	lockdep_assert_held(&irq_lock);
+
+	list_for_each_entry(walk, &active_fds, list) {
+		if (walk->fd == fd)
+			return walk;
+	}
+
+	return NULL;
+}
+
+static void free_irq_entry(struct irq_entry *to_free, bool remove)
+{
+	if (!to_free)
+		return;
+
+	if (remove)
+		os_del_epoll_fd(to_free->fd);
+	list_del(&to_free->list);
+	kfree(to_free);
+}
+
+static bool update_irq_entry(struct irq_entry *entry)
+{
+	enum um_irq_type i;
+	int events = 0;
+
+	for (i = 0; i < NUM_IRQ_TYPES; i++)
+		events |= entry->reg[i].events;
+
+	if (events) {
+		/* will modify (instead of add) if needed */
+		os_add_epoll_fd(events, entry->fd, entry);
+		return true;
+	}
+
+	os_del_epoll_fd(entry->fd);
+	return false;
+}
+
+static void update_or_free_irq_entry(struct irq_entry *entry)
+{
+	if (!update_irq_entry(entry))
+		free_irq_entry(entry, false);
+}
+
+static int activate_fd(int irq, int fd, enum um_irq_type type, void *dev_id,
+		       void (*timetravel_handler)(int, int, void *,
+						  struct time_travel_event *))
+{
+	struct irq_entry *irq_entry;
+	int err, events = os_event_mask(type);
+	unsigned long flags;
+
+	err = os_set_fd_async(fd);
+	if (err < 0)
+		goto out;
+
+	spin_lock_irqsave(&irq_lock, flags);
+	irq_entry = get_irq_entry_by_fd(fd);
+	if (irq_entry) {
+		/* cannot register the same FD twice with the same type */
+		if (WARN_ON(irq_entry->reg[type].events)) {
+			err = -EALREADY;
+			goto out_unlock;
+		}
+
+		/* temporarily disable to avoid IRQ-side locking */
+		os_del_epoll_fd(fd);
+	} else {
+		irq_entry = kzalloc(sizeof(*irq_entry), GFP_ATOMIC);
+		if (!irq_entry) {
+			err = -ENOMEM;
+			goto out_unlock;
+		}
+		irq_entry->fd = fd;
+		list_add_tail(&irq_entry->list, &active_fds);
+		maybe_sigio_broken(fd);
+	}
+
+	irq_entry->reg[type].id = dev_id;
+	irq_entry->reg[type].irq = irq;
+	irq_entry->reg[type].active = true;
+	irq_entry->reg[type].events = events;
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+	if (um_irq_timetravel_handler_used()) {
+		irq_entry->reg[type].timetravel_handler = timetravel_handler;
+		irq_entry->reg[type].event.fn = irq_event_handler;
+	}
+#endif
+
+	WARN_ON(!update_irq_entry(irq_entry));
+	spin_unlock_irqrestore(&irq_lock, flags);
+
+	return 0;
+out_unlock:
+	spin_unlock_irqrestore(&irq_lock, flags);
+out:
+	return err;
+}
+
+/*
+ * Remove the entry or entries for a specific FD, if you
+ * don't want to remove all the possible entries then use
+ * um_free_irq() or deactivate_fd() instead.
+ */
+void free_irq_by_fd(int fd)
+{
+	struct irq_entry *to_free;
+	unsigned long flags;
+
+	spin_lock_irqsave(&irq_lock, flags);
+	to_free = get_irq_entry_by_fd(fd);
+	free_irq_entry(to_free, true);
+	spin_unlock_irqrestore(&irq_lock, flags);
+}
+EXPORT_SYMBOL(free_irq_by_fd);
+
+static void free_irq_by_irq_and_dev(unsigned int irq, void *dev)
+{
+	struct irq_entry *entry;
+	unsigned long flags;
+
+	spin_lock_irqsave(&irq_lock, flags);
+	list_for_each_entry(entry, &active_fds, list) {
+		enum um_irq_type i;
+
+		for (i = 0; i < NUM_IRQ_TYPES; i++) {
+			struct irq_reg *reg = &entry->reg[i];
+
+			if (!reg->events)
+				continue;
+			if (reg->irq != irq)
+				continue;
+			if (reg->id != dev)
+				continue;
+
+			os_del_epoll_fd(entry->fd);
+			reg->events = 0;
+			update_or_free_irq_entry(entry);
+			goto out;
+		}
+	}
+out:
+	spin_unlock_irqrestore(&irq_lock, flags);
+}
+
+void deactivate_fd(int fd, int irqnum)
+{
+	struct irq_entry *entry;
+	unsigned long flags;
+	enum um_irq_type i;
+
+	os_del_epoll_fd(fd);
+
+	spin_lock_irqsave(&irq_lock, flags);
+	entry = get_irq_entry_by_fd(fd);
+	if (!entry)
+		goto out;
+
+	for (i = 0; i < NUM_IRQ_TYPES; i++) {
+		if (!entry->reg[i].events)
+			continue;
+		if (entry->reg[i].irq == irqnum)
+			entry->reg[i].events = 0;
+	}
+
+	update_or_free_irq_entry(entry);
+out:
+	spin_unlock_irqrestore(&irq_lock, flags);
+
+	ignore_sigio_fd(fd);
+}
+EXPORT_SYMBOL(deactivate_fd);
+
+/*
+ * Called just before shutdown in order to provide a clean exec
+ * environment in case the system is rebooting.  No locking because
+ * that would cause a pointless shutdown hang if something hadn't
+ * released the lock.
+ */
+int deactivate_all_fds(void)
+{
+	struct irq_entry *entry;
+
+	/* Stop IO. The IRQ loop has no lock so this is our
+	 * only way of making sure we are safe to dispose
+	 * of all IRQ handlers
+	 */
+	os_set_ioignore();
+
+	/* we can no longer call kfree() here so just deactivate */
+	list_for_each_entry(entry, &active_fds, list)
+		os_del_epoll_fd(entry->fd);
+	os_close_epoll_fd();
+	return 0;
+}
+
+/*
+ * do_IRQ handles all normal device IRQs (the special
+ * SMP cross-CPU interrupts have their own specific
+ * handlers).
+ */
+unsigned int do_IRQ(int irq, struct uml_pt_regs *regs)
+{
+	struct pt_regs *old_regs = set_irq_regs((struct pt_regs *)regs);
+	irq_enter();
+	generic_handle_irq(irq);
+	irq_exit();
+	set_irq_regs(old_regs);
+	return 1;
+}
+
+void um_free_irq(int irq, void *dev)
+{
+	if (WARN(irq < 0 || irq > UM_LAST_SIGNAL_IRQ,
+		 "freeing invalid irq %d", irq))
+		return;
+
+	free_irq_by_irq_and_dev(irq, dev);
+	free_irq(irq, dev);
+	clear_bit(irq, irqs_allocated);
+}
+EXPORT_SYMBOL(um_free_irq);
+
+static int
+_um_request_irq(int irq, int fd, enum um_irq_type type,
+		irq_handler_t handler, unsigned long irqflags,
+		const char *devname, void *dev_id,
+		void (*timetravel_handler)(int, int, void *,
+					   struct time_travel_event *))
+{
+	int err;
+
+	if (irq == UM_IRQ_ALLOC) {
+		int i;
+
+		for (i = UM_FIRST_DYN_IRQ; i < NR_IRQS; i++) {
+			if (!test_and_set_bit(i, irqs_allocated)) {
+				irq = i;
+				break;
+			}
+		}
+	}
+
+	if (irq < 0)
+		return -ENOSPC;
+
+	if (fd != -1) {
+		err = activate_fd(irq, fd, type, dev_id, timetravel_handler);
+		if (err)
+			goto error;
+	}
+
+	err = request_irq(irq, handler, irqflags, devname, dev_id);
+	if (err < 0)
+		goto error;
+
+	return irq;
+error:
+	clear_bit(irq, irqs_allocated);
+	return err;
+}
+
+int um_request_irq(int irq, int fd, enum um_irq_type type,
+		   irq_handler_t handler, unsigned long irqflags,
+		   const char *devname, void *dev_id)
+{
+	return _um_request_irq(irq, fd, type, handler, irqflags,
+			       devname, dev_id, NULL);
+}
+EXPORT_SYMBOL(um_request_irq);
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+int um_request_irq_tt(int irq, int fd, enum um_irq_type type,
+		      irq_handler_t handler, unsigned long irqflags,
+		      const char *devname, void *dev_id,
+		      void (*timetravel_handler)(int, int, void *,
+						 struct time_travel_event *))
+{
+	return _um_request_irq(irq, fd, type, handler, irqflags,
+			       devname, dev_id, timetravel_handler);
+}
+EXPORT_SYMBOL(um_request_irq_tt);
+
+void sigio_run_timetravel_handlers(void)
+{
+	_sigio_handler(NULL, true);
+}
+#endif
+
+#ifdef CONFIG_PM_SLEEP
+void um_irqs_suspend(void)
+{
+	struct irq_entry *entry;
+	unsigned long flags;
+
+	irqs_suspended = true;
+
+	spin_lock_irqsave(&irq_lock, flags);
+	list_for_each_entry(entry, &active_fds, list) {
+		enum um_irq_type t;
+		bool clear = true;
+
+		for (t = 0; t < NUM_IRQ_TYPES; t++) {
+			if (!entry->reg[t].events)
+				continue;
+
+			/*
+			 * For the SIGIO_WRITE_IRQ, which is used to handle the
+			 * SIGIO workaround thread, we need special handling:
+			 * enable wake for it itself, but below we tell it about
+			 * any FDs that should be suspended.
+			 */
+			if (entry->reg[t].wakeup ||
+			    entry->reg[t].irq == SIGIO_WRITE_IRQ
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+			    || entry->reg[t].timetravel_handler
+#endif
+			    ) {
+				clear = false;
+				break;
+			}
+		}
+
+		if (clear) {
+			entry->suspended = true;
+			os_clear_fd_async(entry->fd);
+			entry->sigio_workaround =
+				!__ignore_sigio_fd(entry->fd);
+		}
+	}
+	spin_unlock_irqrestore(&irq_lock, flags);
+}
+
+void um_irqs_resume(void)
+{
+	struct irq_entry *entry;
+	unsigned long flags;
+
+
+	local_irq_save(flags);
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+	/*
+	 * We don't need to lock anything here since we're in resume
+	 * and nothing else is running, but have disabled IRQs so we
+	 * don't try anything else with the interrupt list from there.
+	 */
+	list_for_each_entry(entry, &active_fds, list) {
+		enum um_irq_type t;
+
+		for (t = 0; t < NUM_IRQ_TYPES; t++) {
+			struct irq_reg *reg = &entry->reg[t];
+
+			if (reg->pending_on_resume) {
+				irq_enter();
+				generic_handle_irq(reg->irq);
+				irq_exit();
+				reg->pending_on_resume = false;
+			}
+		}
+	}
+#endif
+
+	spin_lock(&irq_lock);
+	list_for_each_entry(entry, &active_fds, list) {
+		if (entry->suspended) {
+			int err = os_set_fd_async(entry->fd);
+
+			WARN(err < 0, "os_set_fd_async returned %d\n", err);
+			entry->suspended = false;
+
+			if (entry->sigio_workaround) {
+				err = __add_sigio_fd(entry->fd);
+				WARN(err < 0, "add_sigio_returned %d\n", err);
+			}
+		}
+	}
+	spin_unlock_irqrestore(&irq_lock, flags);
+
+	irqs_suspended = false;
+	send_sigio_to_self();
+}
+
+static int normal_irq_set_wake(struct irq_data *d, unsigned int on)
+{
+	struct irq_entry *entry;
+	unsigned long flags;
+
+	spin_lock_irqsave(&irq_lock, flags);
+	list_for_each_entry(entry, &active_fds, list) {
+		enum um_irq_type t;
+
+		for (t = 0; t < NUM_IRQ_TYPES; t++) {
+			if (!entry->reg[t].events)
+				continue;
+
+			if (entry->reg[t].irq != d->irq)
+				continue;
+			entry->reg[t].wakeup = on;
+			goto unlock;
+		}
+	}
+unlock:
+	spin_unlock_irqrestore(&irq_lock, flags);
+	return 0;
+}
+#else
+#define normal_irq_set_wake NULL
+#endif
+
+/*
+ * irq_chip must define at least enable/disable and ack when
+ * the edge handler is used.
+ */
+static void dummy(struct irq_data *d)
+{
+}
+
+/* This is used for everything other than the timer. */
+static struct irq_chip normal_irq_type = {
+	.name = "SIGIO",
+	.irq_disable = dummy,
+	.irq_enable = dummy,
+	.irq_ack = dummy,
+	.irq_mask = dummy,
+	.irq_unmask = dummy,
+	.irq_set_wake = normal_irq_set_wake,
+};
+
+static struct irq_chip alarm_irq_type = {
+	.name = "SIGALRM",
+	.irq_disable = dummy,
+	.irq_enable = dummy,
+	.irq_ack = dummy,
+	.irq_mask = dummy,
+	.irq_unmask = dummy,
+};
+
+void __init init_IRQ(void)
+{
+	int i;
+
+	irq_set_chip_and_handler(TIMER_IRQ, &alarm_irq_type, handle_edge_irq);
+
+	for (i = 1; i < UM_LAST_SIGNAL_IRQ; i++)
+		irq_set_chip_and_handler(i, &normal_irq_type, handle_edge_irq);
+	/* Initialize EPOLL Loop */
+	os_setup_epoll();
+}
+
+/*
+ * IRQ stack entry and exit:
+ *
+ * Unlike i386, UML doesn't receive IRQs on the normal kernel stack
+ * and switch over to the IRQ stack after some preparation.  We use
+ * sigaltstack to receive signals on a separate stack from the start.
+ * These two functions make sure the rest of the kernel won't be too
+ * upset by being on a different stack.  The IRQ stack has a
+ * thread_info structure at the bottom so that current et al continue
+ * to work.
+ *
+ * to_irq_stack copies the current task's thread_info to the IRQ stack
+ * thread_info and sets the tasks's stack to point to the IRQ stack.
+ *
+ * from_irq_stack copies the thread_info struct back (flags may have
+ * been modified) and resets the task's stack pointer.
+ *
+ * Tricky bits -
+ *
+ * What happens when two signals race each other?  UML doesn't block
+ * signals with sigprocmask, SA_DEFER, or sa_mask, so a second signal
+ * could arrive while a previous one is still setting up the
+ * thread_info.
+ *
+ * There are three cases -
+ *     The first interrupt on the stack - sets up the thread_info and
+ * handles the interrupt
+ *     A nested interrupt interrupting the copying of the thread_info -
+ * can't handle the interrupt, as the stack is in an unknown state
+ *     A nested interrupt not interrupting the copying of the
+ * thread_info - doesn't do any setup, just handles the interrupt
+ *
+ * The first job is to figure out whether we interrupted stack setup.
+ * This is done by xchging the signal mask with thread_info->pending.
+ * If the value that comes back is zero, then there is no setup in
+ * progress, and the interrupt can be handled.  If the value is
+ * non-zero, then there is stack setup in progress.  In order to have
+ * the interrupt handled, we leave our signal in the mask, and it will
+ * be handled by the upper handler after it has set up the stack.
+ *
+ * Next is to figure out whether we are the outer handler or a nested
+ * one.  As part of setting up the stack, thread_info->real_thread is
+ * set to non-NULL (and is reset to NULL on exit).  This is the
+ * nesting indicator.  If it is non-NULL, then the stack is already
+ * set up and the handler can run.
+ */
+
+static unsigned long pending_mask;
+
+unsigned long to_irq_stack(unsigned long *mask_out)
+{
+	struct thread_info *ti;
+	unsigned long mask, old;
+	int nested;
+
+	mask = xchg(&pending_mask, *mask_out);
+	if (mask != 0) {
+		/*
+		 * If any interrupts come in at this point, we want to
+		 * make sure that their bits aren't lost by our
+		 * putting our bit in.  So, this loop accumulates bits
+		 * until xchg returns the same value that we put in.
+		 * When that happens, there were no new interrupts,
+		 * and pending_mask contains a bit for each interrupt
+		 * that came in.
+		 */
+		old = *mask_out;
+		do {
+			old |= mask;
+			mask = xchg(&pending_mask, old);
+		} while (mask != old);
+		return 1;
+	}
+
+	ti = current_thread_info();
+	nested = (ti->real_thread != NULL);
+	if (!nested) {
+		struct task_struct *task;
+		struct thread_info *tti;
+
+		task = cpu_tasks[ti->cpu].task;
+		tti = task_thread_info(task);
+
+		*ti = *tti;
+		ti->real_thread = tti;
+		task->stack = ti;
+	}
+
+	mask = xchg(&pending_mask, 0);
+	*mask_out |= mask | nested;
+	return 0;
+}
+
+unsigned long from_irq_stack(int nested)
+{
+	struct thread_info *ti, *to;
+	unsigned long mask;
+
+	ti = current_thread_info();
+
+	pending_mask = 1;
+
+	to = ti->real_thread;
+	current->stack = to;
+	ti->real_thread = NULL;
+	*to = *ti;
+
+	mask = xchg(&pending_mask, 0);
+	return mask & ~1;
+}
+
diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
new file mode 100644
index 000000000..0224fcb36
--- /dev/null
+++ b/arch/um/kernel/kmsg_dump.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kmsg_dump.h>
+#include <linux/spinlock.h>
+#include <linux/console.h>
+#include <linux/string.h>
+#include <shared/init.h>
+#include <shared/kern.h>
+#include <os.h>
+
+static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
+				enum kmsg_dump_reason reason)
+{
+	static struct kmsg_dump_iter iter;
+	static DEFINE_SPINLOCK(lock);
+	static char line[1024];
+	struct console *con;
+	unsigned long flags;
+	size_t len = 0;
+
+	/* only dump kmsg when no console is available */
+	if (!console_trylock())
+		return;
+
+	for_each_console(con) {
+		if(strcmp(con->name, "tty") == 0 &&
+		   (con->flags & (CON_ENABLED | CON_CONSDEV)) != 0) {
+			break;
+		}
+	}
+
+	console_unlock();
+
+	if (con)
+		return;
+
+	if (!spin_trylock_irqsave(&lock, flags))
+		return;
+
+	kmsg_dump_rewind(&iter);
+
+	printf("kmsg_dump:\n");
+	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
+		line[len] = '\0';
+		printf("%s", line);
+	}
+
+	spin_unlock_irqrestore(&lock, flags);
+}
+
+static struct kmsg_dumper kmsg_dumper = {
+	.dump = kmsg_dumper_stdout
+};
+
+int __init kmsg_dumper_stdout_init(void)
+{
+	return kmsg_dump_register(&kmsg_dumper);
+}
+
+__uml_postsetup(kmsg_dumper_stdout_init);
diff --git a/arch/um/kernel/ksyms.c b/arch/um/kernel/ksyms.c
new file mode 100644
index 000000000..3a85bde3e
--- /dev/null
+++ b/arch/um/kernel/ksyms.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/* 
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/module.h>
+#include <os.h>
+
+EXPORT_SYMBOL(um_set_signals);
+EXPORT_SYMBOL(signals_enabled);
+
+EXPORT_SYMBOL(os_stat_fd);
+EXPORT_SYMBOL(os_stat_file);
+EXPORT_SYMBOL(os_access);
+EXPORT_SYMBOL(os_set_exec_close);
+EXPORT_SYMBOL(os_getpid);
+EXPORT_SYMBOL(os_open_file);
+EXPORT_SYMBOL(os_read_file);
+EXPORT_SYMBOL(os_write_file);
+EXPORT_SYMBOL(os_seek_file);
+EXPORT_SYMBOL(os_lock_file);
+EXPORT_SYMBOL(os_ioctl_generic);
+EXPORT_SYMBOL(os_pipe);
+EXPORT_SYMBOL(os_file_type);
+EXPORT_SYMBOL(os_file_mode);
+EXPORT_SYMBOL(os_file_size);
+EXPORT_SYMBOL(os_flush_stdout);
+EXPORT_SYMBOL(os_close_file);
+EXPORT_SYMBOL(os_set_fd_async);
+EXPORT_SYMBOL(os_set_fd_block);
+EXPORT_SYMBOL(helper_wait);
+EXPORT_SYMBOL(os_shutdown_socket);
+EXPORT_SYMBOL(os_create_unix_socket);
+EXPORT_SYMBOL(os_connect_socket);
+EXPORT_SYMBOL(os_accept_connection);
+EXPORT_SYMBOL(os_rcv_fd);
+EXPORT_SYMBOL(run_helper);
+EXPORT_SYMBOL(os_major);
+EXPORT_SYMBOL(os_minor);
+EXPORT_SYMBOL(os_makedev);
+EXPORT_SYMBOL(os_eventfd);
+EXPORT_SYMBOL(os_sendmsg_fds);
+
+EXPORT_SYMBOL(add_sigio_fd);
+EXPORT_SYMBOL(ignore_sigio_fd);
+EXPORT_SYMBOL(sigio_broken);
+
+EXPORT_SYMBOL(syscall);
diff --git a/arch/um/kernel/load_file.c b/arch/um/kernel/load_file.c
new file mode 100644
index 000000000..5cecd0e29
--- /dev/null
+++ b/arch/um/kernel/load_file.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+#include <linux/memblock.h>
+#include <os.h>
+
+#include "um_arch.h"
+
+static int __init __uml_load_file(const char *filename, void *buf, int size)
+{
+	int fd, n;
+
+	fd = os_open_file(filename, of_read(OPENFLAGS()), 0);
+	if (fd < 0) {
+		printk(KERN_ERR "Opening '%s' failed - err = %d\n", filename,
+		       -fd);
+		return -1;
+	}
+	n = os_read_file(fd, buf, size);
+	if (n != size) {
+		printk(KERN_ERR "Read of %d bytes from '%s' failed, "
+		       "err = %d\n", size,
+		       filename, -n);
+		return -1;
+	}
+
+	os_close_file(fd);
+	return 0;
+}
+
+void *uml_load_file(const char *filename, unsigned long long *size)
+{
+	void *area;
+	int err;
+
+	*size = 0;
+
+	if (!filename)
+		return NULL;
+
+	err = os_file_size(filename, size);
+	if (err)
+		return NULL;
+
+	if (*size == 0) {
+		printk(KERN_ERR "\"%s\" is empty\n", filename);
+		return NULL;
+	}
+
+	area = memblock_alloc(*size, SMP_CACHE_BYTES);
+	if (!area)
+		panic("%s: Failed to allocate %llu bytes\n", __func__, *size);
+
+	if (__uml_load_file(filename, area, *size)) {
+		memblock_free(area, *size);
+		return NULL;
+	}
+
+	return area;
+}
diff --git a/arch/um/kernel/maccess.c b/arch/um/kernel/maccess.c
new file mode 100644
index 000000000..8ccd56813
--- /dev/null
+++ b/arch/um/kernel/maccess.c
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2013 Richard Weinberger <richrd@nod.at>
+ */
+
+#include <linux/uaccess.h>
+#include <linux/kernel.h>
+#include <os.h>
+
+bool copy_from_kernel_nofault_allowed(const void *src, size_t size)
+{
+	void *psrc = (void *)rounddown((unsigned long)src, PAGE_SIZE);
+
+	if ((unsigned long)src < PAGE_SIZE || size <= 0)
+		return false;
+	if (os_mincore(psrc, size + src - psrc) <= 0)
+		return false;
+	return true;
+}
diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
new file mode 100644
index 000000000..38d5a71a5
--- /dev/null
+++ b/arch/um/kernel/mem.c
@@ -0,0 +1,238 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/stddef.h>
+#include <linux/module.h>
+#include <linux/memblock.h>
+#include <linux/highmem.h>
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/slab.h>
+#include <asm/fixmap.h>
+#include <asm/page.h>
+#include <as-layout.h>
+#include <init.h>
+#include <kern.h>
+#include <kern_util.h>
+#include <mem_user.h>
+#include <os.h>
+#include <linux/sched/task.h>
+
+#ifdef CONFIG_KASAN
+int kasan_um_is_ready;
+void kasan_init(void)
+{
+	/*
+	 * kasan_map_memory will map all of the required address space and
+	 * the host machine will allocate physical memory as necessary.
+	 */
+	kasan_map_memory((void *)KASAN_SHADOW_START, KASAN_SHADOW_SIZE);
+	init_task.kasan_depth = 0;
+	kasan_um_is_ready = true;
+}
+
+static void (*kasan_init_ptr)(void)
+__section(".kasan_init") __used
+= kasan_init;
+#endif
+
+/* allocated in paging_init, zeroed in mem_init, and unchanged thereafter */
+unsigned long *empty_zero_page = NULL;
+EXPORT_SYMBOL(empty_zero_page);
+
+/*
+ * Initialized during boot, and readonly for initializing page tables
+ * afterwards
+ */
+pgd_t swapper_pg_dir[PTRS_PER_PGD];
+
+/* Initialized at boot time, and readonly after that */
+unsigned long long highmem;
+EXPORT_SYMBOL(highmem);
+int kmalloc_ok = 0;
+
+/* Used during early boot */
+static unsigned long brk_end;
+
+void __init mem_init(void)
+{
+	/* clear the zero-page */
+	memset(empty_zero_page, 0, PAGE_SIZE);
+
+	/* Map in the area just after the brk now that kmalloc is about
+	 * to be turned on.
+	 */
+	brk_end = (unsigned long) UML_ROUND_UP(sbrk(0));
+	map_memory(brk_end, __pa(brk_end), uml_reserved - brk_end, 1, 1, 0);
+	memblock_free((void *)brk_end, uml_reserved - brk_end);
+	uml_reserved = brk_end;
+
+	/* this will put all low memory onto the freelists */
+	memblock_free_all();
+	max_low_pfn = totalram_pages();
+	max_pfn = max_low_pfn;
+	kmalloc_ok = 1;
+}
+
+/*
+ * Create a page table and place a pointer to it in a middle page
+ * directory entry.
+ */
+static void __init one_page_table_init(pmd_t *pmd)
+{
+	if (pmd_none(*pmd)) {
+		pte_t *pte = (pte_t *) memblock_alloc_low(PAGE_SIZE,
+							  PAGE_SIZE);
+		if (!pte)
+			panic("%s: Failed to allocate %lu bytes align=%lx\n",
+			      __func__, PAGE_SIZE, PAGE_SIZE);
+
+		set_pmd(pmd, __pmd(_KERNPG_TABLE +
+					   (unsigned long) __pa(pte)));
+		BUG_ON(pte != pte_offset_kernel(pmd, 0));
+	}
+}
+
+static void __init one_md_table_init(pud_t *pud)
+{
+#ifdef CONFIG_3_LEVEL_PGTABLES
+	pmd_t *pmd_table = (pmd_t *) memblock_alloc_low(PAGE_SIZE, PAGE_SIZE);
+	if (!pmd_table)
+		panic("%s: Failed to allocate %lu bytes align=%lx\n",
+		      __func__, PAGE_SIZE, PAGE_SIZE);
+
+	set_pud(pud, __pud(_KERNPG_TABLE + (unsigned long) __pa(pmd_table)));
+	BUG_ON(pmd_table != pmd_offset(pud, 0));
+#endif
+}
+
+static void __init fixrange_init(unsigned long start, unsigned long end,
+				 pgd_t *pgd_base)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	int i, j;
+	unsigned long vaddr;
+
+	vaddr = start;
+	i = pgd_index(vaddr);
+	j = pmd_index(vaddr);
+	pgd = pgd_base + i;
+
+	for ( ; (i < PTRS_PER_PGD) && (vaddr < end); pgd++, i++) {
+		p4d = p4d_offset(pgd, vaddr);
+		pud = pud_offset(p4d, vaddr);
+		if (pud_none(*pud))
+			one_md_table_init(pud);
+		pmd = pmd_offset(pud, vaddr);
+		for (; (j < PTRS_PER_PMD) && (vaddr < end); pmd++, j++) {
+			one_page_table_init(pmd);
+			vaddr += PMD_SIZE;
+		}
+		j = 0;
+	}
+}
+
+static void __init fixaddr_user_init( void)
+{
+#ifdef CONFIG_ARCH_REUSE_HOST_VSYSCALL_AREA
+	long size = FIXADDR_USER_END - FIXADDR_USER_START;
+	pte_t *pte;
+	phys_t p;
+	unsigned long v, vaddr = FIXADDR_USER_START;
+
+	if (!size)
+		return;
+
+	fixrange_init( FIXADDR_USER_START, FIXADDR_USER_END, swapper_pg_dir);
+	v = (unsigned long) memblock_alloc_low(size, PAGE_SIZE);
+	if (!v)
+		panic("%s: Failed to allocate %lu bytes align=%lx\n",
+		      __func__, size, PAGE_SIZE);
+
+	memcpy((void *) v , (void *) FIXADDR_USER_START, size);
+	p = __pa(v);
+	for ( ; size > 0; size -= PAGE_SIZE, vaddr += PAGE_SIZE,
+		      p += PAGE_SIZE) {
+		pte = virt_to_kpte(vaddr);
+		pte_set_val(*pte, p, PAGE_READONLY);
+	}
+#endif
+}
+
+void __init paging_init(void)
+{
+	unsigned long max_zone_pfn[MAX_NR_ZONES] = { 0 };
+	unsigned long vaddr;
+
+	empty_zero_page = (unsigned long *) memblock_alloc_low(PAGE_SIZE,
+							       PAGE_SIZE);
+	if (!empty_zero_page)
+		panic("%s: Failed to allocate %lu bytes align=%lx\n",
+		      __func__, PAGE_SIZE, PAGE_SIZE);
+
+	max_zone_pfn[ZONE_NORMAL] = end_iomem >> PAGE_SHIFT;
+	free_area_init(max_zone_pfn);
+
+	/*
+	 * Fixed mappings, only the page table structure has to be
+	 * created - mappings will be set by set_fixmap():
+	 */
+	vaddr = __fix_to_virt(__end_of_fixed_addresses - 1) & PMD_MASK;
+	fixrange_init(vaddr, FIXADDR_TOP, swapper_pg_dir);
+
+	fixaddr_user_init();
+}
+
+/*
+ * This can't do anything because nothing in the kernel image can be freed
+ * since it's not in kernel physical memory.
+ */
+
+void free_initmem(void)
+{
+}
+
+/* Allocate and free page tables. */
+
+pgd_t *pgd_alloc(struct mm_struct *mm)
+{
+	pgd_t *pgd = (pgd_t *)__get_free_page(GFP_KERNEL);
+
+	if (pgd) {
+		memset(pgd, 0, USER_PTRS_PER_PGD * sizeof(pgd_t));
+		memcpy(pgd + USER_PTRS_PER_PGD,
+		       swapper_pg_dir + USER_PTRS_PER_PGD,
+		       (PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
+	}
+	return pgd;
+}
+
+void *uml_kmalloc(int size, int flags)
+{
+	return kmalloc(size, flags);
+}
+
+static const pgprot_t protection_map[16] = {
+	[VM_NONE]					= PAGE_NONE,
+	[VM_READ]					= PAGE_READONLY,
+	[VM_WRITE]					= PAGE_COPY,
+	[VM_WRITE | VM_READ]				= PAGE_COPY,
+	[VM_EXEC]					= PAGE_READONLY,
+	[VM_EXEC | VM_READ]				= PAGE_READONLY,
+	[VM_EXEC | VM_WRITE]				= PAGE_COPY,
+	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_COPY,
+	[VM_SHARED]					= PAGE_NONE,
+	[VM_SHARED | VM_READ]				= PAGE_READONLY,
+	[VM_SHARED | VM_WRITE]				= PAGE_SHARED,
+	[VM_SHARED | VM_WRITE | VM_READ]		= PAGE_SHARED,
+	[VM_SHARED | VM_EXEC]				= PAGE_READONLY,
+	[VM_SHARED | VM_EXEC | VM_READ]			= PAGE_READONLY,
+	[VM_SHARED | VM_EXEC | VM_WRITE]		= PAGE_SHARED,
+	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= PAGE_SHARED
+};
+DECLARE_VM_GET_PAGE_PROT
diff --git a/arch/um/kernel/physmem.c b/arch/um/kernel/physmem.c
new file mode 100644
index 000000000..91485119a
--- /dev/null
+++ b/arch/um/kernel/physmem.c
@@ -0,0 +1,222 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/module.h>
+#include <linux/memblock.h>
+#include <linux/mm.h>
+#include <linux/pfn.h>
+#include <asm/page.h>
+#include <asm/sections.h>
+#include <as-layout.h>
+#include <init.h>
+#include <kern.h>
+#include <mem_user.h>
+#include <os.h>
+
+static int physmem_fd = -1;
+
+/* Changed during early boot */
+unsigned long high_physmem;
+EXPORT_SYMBOL(high_physmem);
+
+extern unsigned long long physmem_size;
+
+void __init mem_total_pages(unsigned long physmem, unsigned long iomem,
+		     unsigned long highmem)
+{
+	unsigned long phys_pages, highmem_pages;
+	unsigned long iomem_pages, total_pages;
+
+	phys_pages    = physmem >> PAGE_SHIFT;
+	iomem_pages   = iomem   >> PAGE_SHIFT;
+	highmem_pages = highmem >> PAGE_SHIFT;
+
+	total_pages   = phys_pages + iomem_pages + highmem_pages;
+
+	max_mapnr = total_pages;
+}
+
+void map_memory(unsigned long virt, unsigned long phys, unsigned long len,
+		int r, int w, int x)
+{
+	__u64 offset;
+	int fd, err;
+
+	fd = phys_mapping(phys, &offset);
+	err = os_map_memory((void *) virt, fd, offset, len, r, w, x);
+	if (err) {
+		if (err == -ENOMEM)
+			printk(KERN_ERR "try increasing the host's "
+			       "/proc/sys/vm/max_map_count to <physical "
+			       "memory size>/4096\n");
+		panic("map_memory(0x%lx, %d, 0x%llx, %ld, %d, %d, %d) failed, "
+		      "err = %d\n", virt, fd, offset, len, r, w, x, err);
+	}
+}
+
+/**
+ * setup_physmem() - Setup physical memory for UML
+ * @start:	Start address of the physical kernel memory,
+ *		i.e start address of the executable image.
+ * @reserve_end:	end address of the physical kernel memory.
+ * @len:	Length of total physical memory that should be mapped/made
+ *		available, in bytes.
+ * @highmem:	Number of highmem bytes that should be mapped/made available.
+ *
+ * Creates an unlinked temporary file of size (len + highmem) and memory maps
+ * it on the last executable image address (uml_reserved).
+ *
+ * The offset is needed as the length of the total physical memory
+ * (len + highmem) includes the size of the memory used be the executable image,
+ * but the mapped-to address is the last address of the executable image
+ * (uml_reserved == end address of executable image).
+ *
+ * The memory mapped memory of the temporary file is used as backing memory
+ * of all user space processes/kernel tasks.
+ */
+void __init setup_physmem(unsigned long start, unsigned long reserve_end,
+			  unsigned long len, unsigned long long highmem)
+{
+	unsigned long reserve = reserve_end - start;
+	long map_size = len - reserve;
+	int err;
+
+	if(map_size <= 0) {
+		os_warn("Too few physical memory! Needed=%lu, given=%lu\n",
+			reserve, len);
+		exit(1);
+	}
+
+	physmem_fd = create_mem_file(len + highmem);
+
+	err = os_map_memory((void *) reserve_end, physmem_fd, reserve,
+			    map_size, 1, 1, 1);
+	if (err < 0) {
+		os_warn("setup_physmem - mapping %ld bytes of memory at 0x%p "
+			"failed - errno = %d\n", map_size,
+			(void *) reserve_end, err);
+		exit(1);
+	}
+
+	/*
+	 * Special kludge - This page will be mapped in to userspace processes
+	 * from physmem_fd, so it needs to be written out there.
+	 */
+	os_seek_file(physmem_fd, __pa(__syscall_stub_start));
+	os_write_file(physmem_fd, __syscall_stub_start, PAGE_SIZE);
+	os_fsync_file(physmem_fd);
+
+	memblock_add(__pa(start), len + highmem);
+	memblock_reserve(__pa(start), reserve);
+
+	min_low_pfn = PFN_UP(__pa(reserve_end));
+	max_low_pfn = min_low_pfn + (map_size >> PAGE_SHIFT);
+}
+
+int phys_mapping(unsigned long phys, unsigned long long *offset_out)
+{
+	int fd = -1;
+
+	if (phys < physmem_size) {
+		fd = physmem_fd;
+		*offset_out = phys;
+	}
+	else if (phys < __pa(end_iomem)) {
+		struct iomem_region *region = iomem_regions;
+
+		while (region != NULL) {
+			if ((phys >= region->phys) &&
+			    (phys < region->phys + region->size)) {
+				fd = region->fd;
+				*offset_out = phys - region->phys;
+				break;
+			}
+			region = region->next;
+		}
+	}
+	else if (phys < __pa(end_iomem) + highmem) {
+		fd = physmem_fd;
+		*offset_out = phys - iomem_size;
+	}
+
+	return fd;
+}
+EXPORT_SYMBOL(phys_mapping);
+
+static int __init uml_mem_setup(char *line, int *add)
+{
+	char *retptr;
+	physmem_size = memparse(line,&retptr);
+	return 0;
+}
+__uml_setup("mem=", uml_mem_setup,
+"mem=<Amount of desired ram>\n"
+"    This controls how much \"physical\" memory the kernel allocates\n"
+"    for the system. The size is specified as a number followed by\n"
+"    one of 'k', 'K', 'm', 'M', which have the obvious meanings.\n"
+"    This is not related to the amount of memory in the host.  It can\n"
+"    be more, and the excess, if it's ever used, will just be swapped out.\n"
+"	Example: mem=64M\n\n"
+);
+
+extern int __init parse_iomem(char *str, int *add);
+
+__uml_setup("iomem=", parse_iomem,
+"iomem=<name>,<file>\n"
+"    Configure <file> as an IO memory region named <name>.\n\n"
+);
+
+/*
+ * This list is constructed in parse_iomem and addresses filled in
+ * setup_iomem, both of which run during early boot.  Afterwards, it's
+ * unchanged.
+ */
+struct iomem_region *iomem_regions;
+
+/* Initialized in parse_iomem and unchanged thereafter */
+int iomem_size;
+
+unsigned long find_iomem(char *driver, unsigned long *len_out)
+{
+	struct iomem_region *region = iomem_regions;
+
+	while (region != NULL) {
+		if (!strcmp(region->driver, driver)) {
+			*len_out = region->size;
+			return region->virt;
+		}
+
+		region = region->next;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(find_iomem);
+
+static int setup_iomem(void)
+{
+	struct iomem_region *region = iomem_regions;
+	unsigned long iomem_start = high_physmem + PAGE_SIZE;
+	int err;
+
+	while (region != NULL) {
+		err = os_map_memory((void *) iomem_start, region->fd, 0,
+				    region->size, 1, 1, 0);
+		if (err)
+			printk(KERN_ERR "Mapping iomem region for driver '%s' "
+			       "failed, errno = %d\n", region->driver, -err);
+		else {
+			region->virt = iomem_start;
+			region->phys = __pa(region->virt);
+		}
+
+		iomem_start += region->size + PAGE_SIZE;
+		region = region->next;
+	}
+
+	return 0;
+}
+
+__initcall(setup_iomem);
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
new file mode 100644
index 000000000..010bc422a
--- /dev/null
+++ b/arch/um/kernel/process.c
@@ -0,0 +1,402 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright 2003 PathScale, Inc.
+ */
+
+#include <linux/stddef.h>
+#include <linux/err.h>
+#include <linux/hardirq.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/personality.h>
+#include <linux/proc_fs.h>
+#include <linux/ptrace.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/sched/task.h>
+#include <linux/sched/task_stack.h>
+#include <linux/seq_file.h>
+#include <linux/tick.h>
+#include <linux/threads.h>
+#include <linux/resume_user_mode.h>
+#include <asm/current.h>
+#include <asm/mmu_context.h>
+#include <linux/uaccess.h>
+#include <as-layout.h>
+#include <kern_util.h>
+#include <os.h>
+#include <skas.h>
+#include <registers.h>
+#include <linux/time-internal.h>
+
+/*
+ * This is a per-cpu array.  A processor only modifies its entry and it only
+ * cares about its entry, so it's OK if another processor is modifying its
+ * entry.
+ */
+struct cpu_task cpu_tasks[NR_CPUS] = { [0 ... NR_CPUS - 1] = { -1, NULL } };
+
+static inline int external_pid(void)
+{
+	/* FIXME: Need to look up userspace_pid by cpu */
+	return userspace_pid[0];
+}
+
+int pid_to_processor_id(int pid)
+{
+	int i;
+
+	for (i = 0; i < ncpus; i++) {
+		if (cpu_tasks[i].pid == pid)
+			return i;
+	}
+	return -1;
+}
+
+void free_stack(unsigned long stack, int order)
+{
+	free_pages(stack, order);
+}
+
+unsigned long alloc_stack(int order, int atomic)
+{
+	unsigned long page;
+	gfp_t flags = GFP_KERNEL;
+
+	if (atomic)
+		flags = GFP_ATOMIC;
+	page = __get_free_pages(flags, order);
+
+	return page;
+}
+
+static inline void set_current(struct task_struct *task)
+{
+	cpu_tasks[task_thread_info(task)->cpu] = ((struct cpu_task)
+		{ external_pid(), task });
+}
+
+extern void arch_switch_to(struct task_struct *to);
+
+void *__switch_to(struct task_struct *from, struct task_struct *to)
+{
+	to->thread.prev_sched = from;
+	set_current(to);
+
+	switch_threads(&from->thread.switch_buf, &to->thread.switch_buf);
+	arch_switch_to(current);
+
+	return current->thread.prev_sched;
+}
+
+void interrupt_end(void)
+{
+	struct pt_regs *regs = &current->thread.regs;
+
+	if (need_resched())
+		schedule();
+	if (test_thread_flag(TIF_SIGPENDING) ||
+	    test_thread_flag(TIF_NOTIFY_SIGNAL))
+		do_signal(regs);
+	if (test_thread_flag(TIF_NOTIFY_RESUME))
+		resume_user_mode_work(regs);
+}
+
+int get_current_pid(void)
+{
+	return task_pid_nr(current);
+}
+
+/*
+ * This is called magically, by its address being stuffed in a jmp_buf
+ * and being longjmp-d to.
+ */
+void new_thread_handler(void)
+{
+	int (*fn)(void *), n;
+	void *arg;
+
+	if (current->thread.prev_sched != NULL)
+		schedule_tail(current->thread.prev_sched);
+	current->thread.prev_sched = NULL;
+
+	fn = current->thread.request.u.thread.proc;
+	arg = current->thread.request.u.thread.arg;
+
+	/*
+	 * callback returns only if the kernel thread execs a process
+	 */
+	n = fn(arg);
+	userspace(&current->thread.regs.regs, current_thread_info()->aux_fp_regs);
+}
+
+/* Called magically, see new_thread_handler above */
+void fork_handler(void)
+{
+	force_flush_all();
+
+	schedule_tail(current->thread.prev_sched);
+
+	/*
+	 * XXX: if interrupt_end() calls schedule, this call to
+	 * arch_switch_to isn't needed. We could want to apply this to
+	 * improve performance. -bb
+	 */
+	arch_switch_to(current);
+
+	current->thread.prev_sched = NULL;
+
+	userspace(&current->thread.regs.regs, current_thread_info()->aux_fp_regs);
+}
+
+int copy_thread(struct task_struct * p, const struct kernel_clone_args *args)
+{
+	unsigned long clone_flags = args->flags;
+	unsigned long sp = args->stack;
+	unsigned long tls = args->tls;
+	void (*handler)(void);
+	int ret = 0;
+
+	p->thread = (struct thread_struct) INIT_THREAD;
+
+	if (!args->fn) {
+	  	memcpy(&p->thread.regs.regs, current_pt_regs(),
+		       sizeof(p->thread.regs.regs));
+		PT_REGS_SET_SYSCALL_RETURN(&p->thread.regs, 0);
+		if (sp != 0)
+			REGS_SP(p->thread.regs.regs.gp) = sp;
+
+		handler = fork_handler;
+
+		arch_copy_thread(&current->thread.arch, &p->thread.arch);
+	} else {
+		get_safe_registers(p->thread.regs.regs.gp, p->thread.regs.regs.fp);
+		p->thread.request.u.thread.proc = args->fn;
+		p->thread.request.u.thread.arg = args->fn_arg;
+		handler = new_thread_handler;
+	}
+
+	new_thread(task_stack_page(p), &p->thread.switch_buf, handler);
+
+	if (!args->fn) {
+		clear_flushed_tls(p);
+
+		/*
+		 * Set a new TLS for the child thread?
+		 */
+		if (clone_flags & CLONE_SETTLS)
+			ret = arch_set_tls(p, tls);
+	}
+
+	return ret;
+}
+
+void initial_thread_cb(void (*proc)(void *), void *arg)
+{
+	int save_kmalloc_ok = kmalloc_ok;
+
+	kmalloc_ok = 0;
+	initial_thread_cb_skas(proc, arg);
+	kmalloc_ok = save_kmalloc_ok;
+}
+
+void um_idle_sleep(void)
+{
+	if (time_travel_mode != TT_MODE_OFF)
+		time_travel_sleep();
+	else
+		os_idle_sleep();
+}
+
+void arch_cpu_idle(void)
+{
+	cpu_tasks[current_thread_info()->cpu].pid = os_getpid();
+	um_idle_sleep();
+	raw_local_irq_enable();
+}
+
+int __cant_sleep(void) {
+	return in_atomic() || irqs_disabled() || in_interrupt();
+	/* Is in_interrupt() really needed? */
+}
+
+int user_context(unsigned long sp)
+{
+	unsigned long stack;
+
+	stack = sp & (PAGE_MASK << CONFIG_KERNEL_STACK_ORDER);
+	return stack != (unsigned long) current_thread_info();
+}
+
+extern exitcall_t __uml_exitcall_begin, __uml_exitcall_end;
+
+void do_uml_exitcalls(void)
+{
+	exitcall_t *call;
+
+	call = &__uml_exitcall_end;
+	while (--call >= &__uml_exitcall_begin)
+		(*call)();
+}
+
+char *uml_strdup(const char *string)
+{
+	return kstrdup(string, GFP_KERNEL);
+}
+EXPORT_SYMBOL(uml_strdup);
+
+int copy_to_user_proc(void __user *to, void *from, int size)
+{
+	return copy_to_user(to, from, size);
+}
+
+int copy_from_user_proc(void *to, void __user *from, int size)
+{
+	return copy_from_user(to, from, size);
+}
+
+int clear_user_proc(void __user *buf, int size)
+{
+	return clear_user(buf, size);
+}
+
+static atomic_t using_sysemu = ATOMIC_INIT(0);
+int sysemu_supported;
+
+void set_using_sysemu(int value)
+{
+	if (value > sysemu_supported)
+		return;
+	atomic_set(&using_sysemu, value);
+}
+
+int get_using_sysemu(void)
+{
+	return atomic_read(&using_sysemu);
+}
+
+static int sysemu_proc_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "%d\n", get_using_sysemu());
+	return 0;
+}
+
+static int sysemu_proc_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, sysemu_proc_show, NULL);
+}
+
+static ssize_t sysemu_proc_write(struct file *file, const char __user *buf,
+				 size_t count, loff_t *pos)
+{
+	char tmp[2];
+
+	if (copy_from_user(tmp, buf, 1))
+		return -EFAULT;
+
+	if (tmp[0] >= '0' && tmp[0] <= '2')
+		set_using_sysemu(tmp[0] - '0');
+	/* We use the first char, but pretend to write everything */
+	return count;
+}
+
+static const struct proc_ops sysemu_proc_ops = {
+	.proc_open	= sysemu_proc_open,
+	.proc_read	= seq_read,
+	.proc_lseek	= seq_lseek,
+	.proc_release	= single_release,
+	.proc_write	= sysemu_proc_write,
+};
+
+int __init make_proc_sysemu(void)
+{
+	struct proc_dir_entry *ent;
+	if (!sysemu_supported)
+		return 0;
+
+	ent = proc_create("sysemu", 0600, NULL, &sysemu_proc_ops);
+
+	if (ent == NULL)
+	{
+		printk(KERN_WARNING "Failed to register /proc/sysemu\n");
+		return 0;
+	}
+
+	return 0;
+}
+
+late_initcall(make_proc_sysemu);
+
+int singlestepping(void * t)
+{
+	struct task_struct *task = t ? t : current;
+
+	if (!test_thread_flag(TIF_SINGLESTEP))
+		return 0;
+
+	if (task->thread.singlestep_syscall)
+		return 1;
+
+	return 2;
+}
+
+/*
+ * Only x86 and x86_64 have an arch_align_stack().
+ * All other arches have "#define arch_align_stack(x) (x)"
+ * in their asm/exec.h
+ * As this is included in UML from asm-um/system-generic.h,
+ * we can use it to behave as the subarch does.
+ */
+#ifndef arch_align_stack
+unsigned long arch_align_stack(unsigned long sp)
+{
+	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
+		sp -= prandom_u32_max(8192);
+	return sp & ~0xf;
+}
+#endif
+
+unsigned long __get_wchan(struct task_struct *p)
+{
+	unsigned long stack_page, sp, ip;
+	bool seen_sched = 0;
+
+	stack_page = (unsigned long) task_stack_page(p);
+	/* Bail if the process has no kernel stack for some reason */
+	if (stack_page == 0)
+		return 0;
+
+	sp = p->thread.switch_buf->JB_SP;
+	/*
+	 * Bail if the stack pointer is below the bottom of the kernel
+	 * stack for some reason
+	 */
+	if (sp < stack_page)
+		return 0;
+
+	while (sp < stack_page + THREAD_SIZE) {
+		ip = *((unsigned long *) sp);
+		if (in_sched_functions(ip))
+			/* Ignore everything until we're above the scheduler */
+			seen_sched = 1;
+		else if (kernel_text_address(ip) && seen_sched)
+			return ip;
+
+		sp += sizeof(unsigned long);
+	}
+
+	return 0;
+}
+
+int elf_core_copy_fpregs(struct task_struct *t, elf_fpregset_t *fpu)
+{
+	int cpu = current_thread_info()->cpu;
+
+	return save_i387_registers(userspace_pid[cpu], (unsigned long *) fpu);
+}
+
diff --git a/arch/um/kernel/ptrace.c b/arch/um/kernel/ptrace.c
new file mode 100644
index 000000000..5154b27de
--- /dev/null
+++ b/arch/um/kernel/ptrace.c
@@ -0,0 +1,157 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/audit.h>
+#include <linux/ptrace.h>
+#include <linux/sched.h>
+#include <linux/uaccess.h>
+#include <asm/ptrace-abi.h>
+
+void user_enable_single_step(struct task_struct *child)
+{
+	set_tsk_thread_flag(child, TIF_SINGLESTEP);
+	child->thread.singlestep_syscall = 0;
+
+#ifdef SUBARCH_SET_SINGLESTEPPING
+	SUBARCH_SET_SINGLESTEPPING(child, 1);
+#endif
+}
+
+void user_disable_single_step(struct task_struct *child)
+{
+	clear_tsk_thread_flag(child, TIF_SINGLESTEP);
+	child->thread.singlestep_syscall = 0;
+
+#ifdef SUBARCH_SET_SINGLESTEPPING
+	SUBARCH_SET_SINGLESTEPPING(child, 0);
+#endif
+}
+
+/*
+ * Called by kernel/ptrace.c when detaching..
+ */
+void ptrace_disable(struct task_struct *child)
+{
+	user_disable_single_step(child);
+}
+
+extern int peek_user(struct task_struct * child, long addr, long data);
+extern int poke_user(struct task_struct * child, long addr, long data);
+
+long arch_ptrace(struct task_struct *child, long request,
+		 unsigned long addr, unsigned long data)
+{
+	int i, ret;
+	unsigned long __user *p = (void __user *)data;
+	void __user *vp = p;
+
+	switch (request) {
+	/* read the word at location addr in the USER area. */
+	case PTRACE_PEEKUSR:
+		ret = peek_user(child, addr, data);
+		break;
+
+	/* write the word at location addr in the USER area */
+	case PTRACE_POKEUSR:
+		ret = poke_user(child, addr, data);
+		break;
+
+	case PTRACE_SYSEMU:
+	case PTRACE_SYSEMU_SINGLESTEP:
+		ret = -EIO;
+		break;
+
+#ifdef PTRACE_GETREGS
+	case PTRACE_GETREGS: { /* Get all gp regs from the child. */
+		if (!access_ok(p, MAX_REG_OFFSET)) {
+			ret = -EIO;
+			break;
+		}
+		for ( i = 0; i < MAX_REG_OFFSET; i += sizeof(long) ) {
+			__put_user(getreg(child, i), p);
+			p++;
+		}
+		ret = 0;
+		break;
+	}
+#endif
+#ifdef PTRACE_SETREGS
+	case PTRACE_SETREGS: { /* Set all gp regs in the child. */
+		unsigned long tmp = 0;
+		if (!access_ok(p, MAX_REG_OFFSET)) {
+			ret = -EIO;
+			break;
+		}
+		for ( i = 0; i < MAX_REG_OFFSET; i += sizeof(long) ) {
+			__get_user(tmp, p);
+			putreg(child, i, tmp);
+			p++;
+		}
+		ret = 0;
+		break;
+	}
+#endif
+	case PTRACE_GET_THREAD_AREA:
+		ret = ptrace_get_thread_area(child, addr, vp);
+		break;
+
+	case PTRACE_SET_THREAD_AREA:
+		ret = ptrace_set_thread_area(child, addr, vp);
+		break;
+
+	default:
+		ret = ptrace_request(child, request, addr, data);
+		if (ret == -EIO)
+			ret = subarch_ptrace(child, request, addr, data);
+		break;
+	}
+
+	return ret;
+}
+
+static void send_sigtrap(struct uml_pt_regs *regs, int error_code)
+{
+	/* Send us the fake SIGTRAP */
+	force_sig_fault(SIGTRAP, TRAP_BRKPT,
+			/* User-mode eip? */
+			UPT_IS_USER(regs) ? (void __user *) UPT_IP(regs) : NULL);
+}
+
+/*
+ * XXX Check TIF_SINGLESTEP for singlestepping check and
+ * PT_PTRACED vs TIF_SYSCALL_TRACE for syscall tracing check
+ */
+int syscall_trace_enter(struct pt_regs *regs)
+{
+	audit_syscall_entry(UPT_SYSCALL_NR(&regs->regs),
+			    UPT_SYSCALL_ARG1(&regs->regs),
+			    UPT_SYSCALL_ARG2(&regs->regs),
+			    UPT_SYSCALL_ARG3(&regs->regs),
+			    UPT_SYSCALL_ARG4(&regs->regs));
+
+	if (!test_thread_flag(TIF_SYSCALL_TRACE))
+		return 0;
+
+	return ptrace_report_syscall_entry(regs);
+}
+
+void syscall_trace_leave(struct pt_regs *regs)
+{
+	int ptraced = current->ptrace;
+
+	audit_syscall_exit(regs);
+
+	/* Fake a debug trap */
+	if (test_thread_flag(TIF_SINGLESTEP))
+		send_sigtrap(&regs->regs, 0);
+
+	if (!test_thread_flag(TIF_SYSCALL_TRACE))
+		return;
+
+	ptrace_report_syscall_exit(regs, 0);
+	/* force do_signal() --> is_syscall() */
+	if (ptraced & PT_PTRACED)
+		set_thread_flag(TIF_SIGPENDING);
+}
diff --git a/arch/um/kernel/reboot.c b/arch/um/kernel/reboot.c
new file mode 100644
index 000000000..48c0610d5
--- /dev/null
+++ b/arch/um/kernel/reboot.c
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+/* 
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/sched/signal.h>
+#include <linux/sched/task.h>
+#include <linux/sched/mm.h>
+#include <linux/spinlock.h>
+#include <linux/slab.h>
+#include <linux/oom.h>
+#include <kern_util.h>
+#include <os.h>
+#include <skas.h>
+
+void (*pm_power_off)(void);
+EXPORT_SYMBOL(pm_power_off);
+
+static void kill_off_processes(void)
+{
+	struct task_struct *p;
+	int pid;
+
+	read_lock(&tasklist_lock);
+	for_each_process(p) {
+		struct task_struct *t;
+
+		t = find_lock_task_mm(p);
+		if (!t)
+			continue;
+		pid = t->mm->context.id.u.pid;
+		task_unlock(t);
+		os_kill_ptraced_process(pid, 1);
+	}
+	read_unlock(&tasklist_lock);
+}
+
+void uml_cleanup(void)
+{
+	kmalloc_ok = 0;
+	do_uml_exitcalls();
+	kill_off_processes();
+}
+
+void machine_restart(char * __unused)
+{
+	uml_cleanup();
+	reboot_skas();
+}
+
+void machine_power_off(void)
+{
+	uml_cleanup();
+	halt_skas();
+}
+
+void machine_halt(void)
+{
+	machine_power_off();
+}
diff --git a/arch/um/kernel/sigio.c b/arch/um/kernel/sigio.c
new file mode 100644
index 000000000..5085a50c3
--- /dev/null
+++ b/arch/um/kernel/sigio.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ */
+
+#include <linux/interrupt.h>
+#include <irq_kern.h>
+#include <os.h>
+#include <sigio.h>
+
+/* Protected by sigio_lock() called from write_sigio_workaround */
+static int sigio_irq_fd = -1;
+
+static irqreturn_t sigio_interrupt(int irq, void *data)
+{
+	char c;
+
+	os_read_file(sigio_irq_fd, &c, sizeof(c));
+	return IRQ_HANDLED;
+}
+
+int write_sigio_irq(int fd)
+{
+	int err;
+
+	err = um_request_irq(SIGIO_WRITE_IRQ, fd, IRQ_READ, sigio_interrupt,
+			     0, "write sigio", NULL);
+	if (err < 0) {
+		printk(KERN_ERR "write_sigio_irq : um_request_irq failed, "
+		       "err = %d\n", err);
+		return -1;
+	}
+	sigio_irq_fd = fd;
+	return 0;
+}
+
+/* These are called from os-Linux/sigio.c to protect its pollfds arrays. */
+static DEFINE_MUTEX(sigio_mutex);
+
+void sigio_lock(void)
+{
+	mutex_lock(&sigio_mutex);
+}
+
+void sigio_unlock(void)
+{
+	mutex_unlock(&sigio_mutex);
+}
diff --git a/arch/um/kernel/signal.c b/arch/um/kernel/signal.c
new file mode 100644
index 000000000..ae4658f57
--- /dev/null
+++ b/arch/um/kernel/signal.c
@@ -0,0 +1,141 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/module.h>
+#include <linux/ptrace.h>
+#include <linux/sched.h>
+#include <linux/ftrace.h>
+#include <asm/siginfo.h>
+#include <asm/signal.h>
+#include <asm/unistd.h>
+#include <frame_kern.h>
+#include <kern_util.h>
+#include <os.h>
+
+EXPORT_SYMBOL(block_signals);
+EXPORT_SYMBOL(unblock_signals);
+
+void block_signals_trace(void)
+{
+	block_signals();
+	if (current_thread_info())
+		trace_hardirqs_off();
+}
+
+void unblock_signals_trace(void)
+{
+	if (current_thread_info())
+		trace_hardirqs_on();
+	unblock_signals();
+}
+
+void um_trace_signals_on(void)
+{
+	if (current_thread_info())
+		trace_hardirqs_on();
+}
+
+void um_trace_signals_off(void)
+{
+	if (current_thread_info())
+		trace_hardirqs_off();
+}
+
+/*
+ * OK, we're invoking a handler
+ */
+static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
+{
+	sigset_t *oldset = sigmask_to_save();
+	int singlestep = 0;
+	unsigned long sp;
+	int err;
+
+	if (test_thread_flag(TIF_SINGLESTEP) && (current->ptrace & PT_PTRACED))
+		singlestep = 1;
+
+	/* Did we come from a system call? */
+	if (PT_REGS_SYSCALL_NR(regs) >= 0) {
+		/* If so, check system call restarting.. */
+		switch (PT_REGS_SYSCALL_RET(regs)) {
+		case -ERESTART_RESTARTBLOCK:
+		case -ERESTARTNOHAND:
+			PT_REGS_SYSCALL_RET(regs) = -EINTR;
+			break;
+
+		case -ERESTARTSYS:
+			if (!(ksig->ka.sa.sa_flags & SA_RESTART)) {
+				PT_REGS_SYSCALL_RET(regs) = -EINTR;
+				break;
+			}
+			fallthrough;
+		case -ERESTARTNOINTR:
+			PT_REGS_RESTART_SYSCALL(regs);
+			PT_REGS_ORIG_SYSCALL(regs) = PT_REGS_SYSCALL_NR(regs);
+			break;
+		}
+	}
+
+	sp = PT_REGS_SP(regs);
+	if ((ksig->ka.sa.sa_flags & SA_ONSTACK) && (sas_ss_flags(sp) == 0))
+		sp = current->sas_ss_sp + current->sas_ss_size;
+
+#ifdef CONFIG_ARCH_HAS_SC_SIGNALS
+	if (!(ksig->ka.sa.sa_flags & SA_SIGINFO))
+		err = setup_signal_stack_sc(sp, ksig, regs, oldset);
+	else
+#endif
+		err = setup_signal_stack_si(sp, ksig, regs, oldset);
+
+	signal_setup_done(err, ksig, singlestep);
+}
+
+void do_signal(struct pt_regs *regs)
+{
+	struct ksignal ksig;
+	int handled_sig = 0;
+
+	while (get_signal(&ksig)) {
+		handled_sig = 1;
+		/* Whee!  Actually deliver the signal.  */
+		handle_signal(&ksig, regs);
+	}
+
+	/* Did we come from a system call? */
+	if (!handled_sig && (PT_REGS_SYSCALL_NR(regs) >= 0)) {
+		/* Restart the system call - no handlers present */
+		switch (PT_REGS_SYSCALL_RET(regs)) {
+		case -ERESTARTNOHAND:
+		case -ERESTARTSYS:
+		case -ERESTARTNOINTR:
+			PT_REGS_ORIG_SYSCALL(regs) = PT_REGS_SYSCALL_NR(regs);
+			PT_REGS_RESTART_SYSCALL(regs);
+			break;
+		case -ERESTART_RESTARTBLOCK:
+			PT_REGS_ORIG_SYSCALL(regs) = __NR_restart_syscall;
+			PT_REGS_RESTART_SYSCALL(regs);
+			break;
+		}
+	}
+
+	/*
+	 * This closes a way to execute a system call on the host.  If
+	 * you set a breakpoint on a system call instruction and singlestep
+	 * from it, the tracing thread used to PTRACE_SINGLESTEP the process
+	 * rather than PTRACE_SYSCALL it, allowing the system call to execute
+	 * on the host.  The tracing thread will check this flag and
+	 * PTRACE_SYSCALL if necessary.
+	 */
+	if (test_thread_flag(TIF_SINGLESTEP))
+		current->thread.singlestep_syscall =
+			is_syscall(PT_REGS_IP(&current->thread.regs));
+
+	/*
+	 * if there's no signal to deliver, we just put the saved sigmask
+	 * back
+	 */
+	if (!handled_sig)
+		restore_saved_sigmask();
+}
diff --git a/arch/um/kernel/skas/Makefile b/arch/um/kernel/skas/Makefile
new file mode 100644
index 000000000..f3d494a4f
--- /dev/null
+++ b/arch/um/kernel/skas/Makefile
@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+#
+
+obj-y := clone.o mmu.o process.o syscall.o uaccess.o
+
+# clone.o is in the stub, so it can't be built with profiling
+# GCC hardened also auto-enables -fpic, but we need %ebx so it can't work ->
+# disable it
+
+CFLAGS_clone.o := $(CFLAGS_NO_HARDENING)
+UNPROFILE_OBJS := clone.o
+
+KCOV_INSTRUMENT := n
+
+include arch/um/scripts/Makefile.rules
diff --git a/arch/um/kernel/skas/clone.c b/arch/um/kernel/skas/clone.c
new file mode 100644
index 000000000..ff5061f29
--- /dev/null
+++ b/arch/um/kernel/skas/clone.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <signal.h>
+#include <sched.h>
+#include <asm/unistd.h>
+#include <sys/time.h>
+#include <as-layout.h>
+#include <ptrace_user.h>
+#include <stub-data.h>
+#include <sysdep/stub.h>
+
+/*
+ * This is in a separate file because it needs to be compiled with any
+ * extraneous gcc flags (-pg, -fprofile-arcs, -ftest-coverage) disabled
+ *
+ * Use UM_KERN_PAGE_SIZE instead of PAGE_SIZE because that calls getpagesize
+ * on some systems.
+ */
+
+void __attribute__ ((__section__ (".__syscall_stub")))
+stub_clone_handler(void)
+{
+	struct stub_data *data = get_stub_page();
+	long err;
+
+	err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD,
+			    (unsigned long)data + UM_KERN_PAGE_SIZE / 2);
+	if (err) {
+		data->parent_err = err;
+		goto done;
+	}
+
+	err = stub_syscall4(__NR_ptrace, PTRACE_TRACEME, 0, 0, 0);
+	if (err) {
+		data->child_err = err;
+		goto done;
+	}
+
+	remap_stack_and_trap();
+
+ done:
+	trap_myself();
+}
diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
new file mode 100644
index 000000000..125df465e
--- /dev/null
+++ b/arch/um/kernel/skas/mmu.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/slab.h>
+
+#include <asm/pgalloc.h>
+#include <asm/sections.h>
+#include <as-layout.h>
+#include <os.h>
+#include <skas.h>
+
+int init_new_context(struct task_struct *task, struct mm_struct *mm)
+{
+ 	struct mm_context *from_mm = NULL;
+	struct mm_context *to_mm = &mm->context;
+	unsigned long stack = 0;
+	int ret = -ENOMEM;
+
+	stack = get_zeroed_page(GFP_KERNEL);
+	if (stack == 0)
+		goto out;
+
+	to_mm->id.stack = stack;
+	if (current->mm != NULL && current->mm != &init_mm)
+		from_mm = &current->mm->context;
+
+	block_signals_trace();
+	if (from_mm)
+		to_mm->id.u.pid = copy_context_skas0(stack,
+						     from_mm->id.u.pid);
+	else to_mm->id.u.pid = start_userspace(stack);
+	unblock_signals_trace();
+
+	if (to_mm->id.u.pid < 0) {
+		ret = to_mm->id.u.pid;
+		goto out_free;
+	}
+
+	ret = init_new_ldt(to_mm, from_mm);
+	if (ret < 0) {
+		printk(KERN_ERR "init_new_context_skas - init_ldt"
+		       " failed, errno = %d\n", ret);
+		goto out_free;
+	}
+
+	return 0;
+
+ out_free:
+	if (to_mm->id.stack != 0)
+		free_page(to_mm->id.stack);
+ out:
+	return ret;
+}
+
+void destroy_context(struct mm_struct *mm)
+{
+	struct mm_context *mmu = &mm->context;
+
+	/*
+	 * If init_new_context wasn't called, this will be
+	 * zero, resulting in a kill(0), which will result in the
+	 * whole UML suddenly dying.  Also, cover negative and
+	 * 1 cases, since they shouldn't happen either.
+	 */
+	if (mmu->id.u.pid < 2) {
+		printk(KERN_ERR "corrupt mm_context - pid = %d\n",
+		       mmu->id.u.pid);
+		return;
+	}
+	os_kill_ptraced_process(mmu->id.u.pid, 1);
+
+	free_page(mmu->id.stack);
+	free_ldt(mmu);
+}
diff --git a/arch/um/kernel/skas/process.c b/arch/um/kernel/skas/process.c
new file mode 100644
index 000000000..f2ac134c9
--- /dev/null
+++ b/arch/um/kernel/skas/process.c
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/init.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/task_stack.h>
+#include <linux/sched/task.h>
+
+#include <as-layout.h>
+#include <kern.h>
+#include <os.h>
+#include <skas.h>
+
+extern void start_kernel(void);
+
+static int __init start_kernel_proc(void *unused)
+{
+	int pid;
+
+	block_signals_trace();
+	pid = os_getpid();
+
+	cpu_tasks[0].pid = pid;
+	cpu_tasks[0].task = current;
+
+	start_kernel();
+	return 0;
+}
+
+extern int userspace_pid[];
+
+extern char cpu0_irqstack[];
+
+int __init start_uml(void)
+{
+	stack_protections((unsigned long) &cpu0_irqstack);
+	set_sigstack(cpu0_irqstack, THREAD_SIZE);
+
+	init_new_thread_signals();
+
+	init_task.thread.request.u.thread.proc = start_kernel_proc;
+	init_task.thread.request.u.thread.arg = NULL;
+	return start_idle_thread(task_stack_page(&init_task),
+				 &init_task.thread.switch_buf);
+}
+
+unsigned long current_stub_stack(void)
+{
+	if (current->mm == NULL)
+		return 0;
+
+	return current->mm->context.id.stack;
+}
diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
new file mode 100644
index 000000000..9ee19e566
--- /dev/null
+++ b/arch/um/kernel/skas/syscall.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/kernel.h>
+#include <linux/ptrace.h>
+#include <linux/seccomp.h>
+#include <kern_util.h>
+#include <sysdep/ptrace.h>
+#include <sysdep/ptrace_user.h>
+#include <sysdep/syscalls.h>
+#include <linux/time-internal.h>
+#include <asm/unistd.h>
+
+void handle_syscall(struct uml_pt_regs *r)
+{
+	struct pt_regs *regs = container_of(r, struct pt_regs, regs);
+	int syscall;
+
+	/*
+	 * If we have infinite CPU resources, then make every syscall also a
+	 * preemption point, since we don't have any other preemption in this
+	 * case, and kernel threads would basically never run until userspace
+	 * went to sleep, even if said userspace interacts with the kernel in
+	 * various ways.
+	 */
+	if (time_travel_mode == TT_MODE_INFCPU ||
+	    time_travel_mode == TT_MODE_EXTERNAL)
+		schedule();
+
+	/* Initialize the syscall number and default return value. */
+	UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
+	PT_REGS_SET_SYSCALL_RETURN(regs, -ENOSYS);
+
+	if (syscall_trace_enter(regs))
+		goto out;
+
+	/* Do the seccomp check after ptrace; failures should be fast. */
+	if (secure_computing() == -1)
+		goto out;
+
+	syscall = UPT_SYSCALL_NR(r);
+	if (syscall >= 0 && syscall < __NR_syscalls)
+		PT_REGS_SET_SYSCALL_RETURN(regs,
+				EXECUTE_SYSCALL(syscall, regs));
+
+out:
+	syscall_trace_leave(regs);
+}
diff --git a/arch/um/kernel/skas/uaccess.c b/arch/um/kernel/skas/uaccess.c
new file mode 100644
index 000000000..aaee96f07
--- /dev/null
+++ b/arch/um/kernel/skas/uaccess.c
@@ -0,0 +1,366 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/err.h>
+#include <linux/highmem.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <asm/current.h>
+#include <asm/page.h>
+#include <kern_util.h>
+#include <asm/futex.h>
+#include <os.h>
+
+pte_t *virt_to_pte(struct mm_struct *mm, unsigned long addr)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+
+	if (mm == NULL)
+		return NULL;
+
+	pgd = pgd_offset(mm, addr);
+	if (!pgd_present(*pgd))
+		return NULL;
+
+	p4d = p4d_offset(pgd, addr);
+	if (!p4d_present(*p4d))
+		return NULL;
+
+	pud = pud_offset(p4d, addr);
+	if (!pud_present(*pud))
+		return NULL;
+
+	pmd = pmd_offset(pud, addr);
+	if (!pmd_present(*pmd))
+		return NULL;
+
+	return pte_offset_kernel(pmd, addr);
+}
+
+static pte_t *maybe_map(unsigned long virt, int is_write)
+{
+	pte_t *pte = virt_to_pte(current->mm, virt);
+	int err, dummy_code;
+
+	if ((pte == NULL) || !pte_present(*pte) ||
+	    (is_write && !pte_write(*pte))) {
+		err = handle_page_fault(virt, 0, is_write, 1, &dummy_code);
+		if (err)
+			return NULL;
+		pte = virt_to_pte(current->mm, virt);
+	}
+	if (!pte_present(*pte))
+		pte = NULL;
+
+	return pte;
+}
+
+static int do_op_one_page(unsigned long addr, int len, int is_write,
+		 int (*op)(unsigned long addr, int len, void *arg), void *arg)
+{
+	struct page *page;
+	pte_t *pte;
+	int n;
+
+	pte = maybe_map(addr, is_write);
+	if (pte == NULL)
+		return -1;
+
+	page = pte_page(*pte);
+#ifdef CONFIG_64BIT
+	pagefault_disable();
+	addr = (unsigned long) page_address(page) +
+		(addr & ~PAGE_MASK);
+#else
+	addr = (unsigned long) kmap_atomic(page) +
+		(addr & ~PAGE_MASK);
+#endif
+	n = (*op)(addr, len, arg);
+
+#ifdef CONFIG_64BIT
+	pagefault_enable();
+#else
+	kunmap_atomic((void *)addr);
+#endif
+
+	return n;
+}
+
+static long buffer_op(unsigned long addr, int len, int is_write,
+		      int (*op)(unsigned long, int, void *), void *arg)
+{
+	long size, remain, n;
+
+	size = min(PAGE_ALIGN(addr) - addr, (unsigned long) len);
+	remain = len;
+
+	n = do_op_one_page(addr, size, is_write, op, arg);
+	if (n != 0) {
+		remain = (n < 0 ? remain : 0);
+		goto out;
+	}
+
+	addr += size;
+	remain -= size;
+	if (remain == 0)
+		goto out;
+
+	while (addr < ((addr + remain) & PAGE_MASK)) {
+		n = do_op_one_page(addr, PAGE_SIZE, is_write, op, arg);
+		if (n != 0) {
+			remain = (n < 0 ? remain : 0);
+			goto out;
+		}
+
+		addr += PAGE_SIZE;
+		remain -= PAGE_SIZE;
+	}
+	if (remain == 0)
+		goto out;
+
+	n = do_op_one_page(addr, remain, is_write, op, arg);
+	if (n != 0) {
+		remain = (n < 0 ? remain : 0);
+		goto out;
+	}
+
+	return 0;
+ out:
+	return remain;
+}
+
+static int copy_chunk_from_user(unsigned long from, int len, void *arg)
+{
+	unsigned long *to_ptr = arg, to = *to_ptr;
+
+	memcpy((void *) to, (void *) from, len);
+	*to_ptr += len;
+	return 0;
+}
+
+unsigned long raw_copy_from_user(void *to, const void __user *from, unsigned long n)
+{
+	return buffer_op((unsigned long) from, n, 0, copy_chunk_from_user, &to);
+}
+EXPORT_SYMBOL(raw_copy_from_user);
+
+static int copy_chunk_to_user(unsigned long to, int len, void *arg)
+{
+	unsigned long *from_ptr = arg, from = *from_ptr;
+
+	memcpy((void *) to, (void *) from, len);
+	*from_ptr += len;
+	return 0;
+}
+
+unsigned long raw_copy_to_user(void __user *to, const void *from, unsigned long n)
+{
+	return buffer_op((unsigned long) to, n, 1, copy_chunk_to_user, &from);
+}
+EXPORT_SYMBOL(raw_copy_to_user);
+
+static int strncpy_chunk_from_user(unsigned long from, int len, void *arg)
+{
+	char **to_ptr = arg, *to = *to_ptr;
+	int n;
+
+	strncpy(to, (void *) from, len);
+	n = strnlen(to, len);
+	*to_ptr += n;
+
+	if (n < len)
+	        return 1;
+	return 0;
+}
+
+long strncpy_from_user(char *dst, const char __user *src, long count)
+{
+	long n;
+	char *ptr = dst;
+
+	if (!access_ok(src, 1))
+		return -EFAULT;
+	n = buffer_op((unsigned long) src, count, 0, strncpy_chunk_from_user,
+		      &ptr);
+	if (n != 0)
+		return -EFAULT;
+	return strnlen(dst, count);
+}
+EXPORT_SYMBOL(strncpy_from_user);
+
+static int clear_chunk(unsigned long addr, int len, void *unused)
+{
+	memset((void *) addr, 0, len);
+	return 0;
+}
+
+unsigned long __clear_user(void __user *mem, unsigned long len)
+{
+	return buffer_op((unsigned long) mem, len, 1, clear_chunk, NULL);
+}
+EXPORT_SYMBOL(__clear_user);
+
+static int strnlen_chunk(unsigned long str, int len, void *arg)
+{
+	int *len_ptr = arg, n;
+
+	n = strnlen((void *) str, len);
+	*len_ptr += n;
+
+	if (n < len)
+		return 1;
+	return 0;
+}
+
+long strnlen_user(const char __user *str, long len)
+{
+	int count = 0, n;
+
+	if (!access_ok(str, 1))
+		return -EFAULT;
+	n = buffer_op((unsigned long) str, len, 0, strnlen_chunk, &count);
+	if (n == 0)
+		return count + 1;
+	return 0;
+}
+EXPORT_SYMBOL(strnlen_user);
+
+/**
+ * arch_futex_atomic_op_inuser() - Atomic arithmetic operation with constant
+ *			  argument and comparison of the previous
+ *			  futex value with another constant.
+ *
+ * @encoded_op:	encoded operation to execute
+ * @uaddr:	pointer to user space address
+ *
+ * Return:
+ * 0 - On success
+ * -EFAULT - User access resulted in a page fault
+ * -EAGAIN - Atomic operation was unable to complete due to contention
+ * -ENOSYS - Operation not supported
+ */
+
+int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
+{
+	int oldval, ret;
+	struct page *page;
+	unsigned long addr = (unsigned long) uaddr;
+	pte_t *pte;
+
+	ret = -EFAULT;
+	if (!access_ok(uaddr, sizeof(*uaddr)))
+		return -EFAULT;
+	preempt_disable();
+	pte = maybe_map(addr, 1);
+	if (pte == NULL)
+		goto out_inuser;
+
+	page = pte_page(*pte);
+#ifdef CONFIG_64BIT
+	pagefault_disable();
+	addr = (unsigned long) page_address(page) +
+			(((unsigned long) addr) & ~PAGE_MASK);
+#else
+	addr = (unsigned long) kmap_atomic(page) +
+		((unsigned long) addr & ~PAGE_MASK);
+#endif
+	uaddr = (u32 *) addr;
+	oldval = *uaddr;
+
+	ret = 0;
+
+	switch (op) {
+	case FUTEX_OP_SET:
+		*uaddr = oparg;
+		break;
+	case FUTEX_OP_ADD:
+		*uaddr += oparg;
+		break;
+	case FUTEX_OP_OR:
+		*uaddr |= oparg;
+		break;
+	case FUTEX_OP_ANDN:
+		*uaddr &= ~oparg;
+		break;
+	case FUTEX_OP_XOR:
+		*uaddr ^= oparg;
+		break;
+	default:
+		ret = -ENOSYS;
+	}
+#ifdef CONFIG_64BIT
+	pagefault_enable();
+#else
+	kunmap_atomic((void *)addr);
+#endif
+
+out_inuser:
+	preempt_enable();
+
+	if (ret == 0)
+		*oval = oldval;
+
+	return ret;
+}
+EXPORT_SYMBOL(arch_futex_atomic_op_inuser);
+
+/**
+ * futex_atomic_cmpxchg_inatomic() - Compare and exchange the content of the
+ *				uaddr with newval if the current value is
+ *				oldval.
+ * @uval:	pointer to store content of @uaddr
+ * @uaddr:	pointer to user space address
+ * @oldval:	old value
+ * @newval:	new value to store to @uaddr
+ *
+ * Return:
+ * 0 - On success
+ * -EFAULT - User access resulted in a page fault
+ * -EAGAIN - Atomic operation was unable to complete due to contention
+ */
+
+int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
+			      u32 oldval, u32 newval)
+{
+	struct page *page;
+	pte_t *pte;
+	int ret = -EFAULT;
+
+	if (!access_ok(uaddr, sizeof(*uaddr)))
+		return -EFAULT;
+
+	preempt_disable();
+	pte = maybe_map((unsigned long) uaddr, 1);
+	if (pte == NULL)
+		goto out_inatomic;
+
+	page = pte_page(*pte);
+#ifdef CONFIG_64BIT
+	pagefault_disable();
+	uaddr = page_address(page) + (((unsigned long) uaddr) & ~PAGE_MASK);
+#else
+	uaddr = kmap_atomic(page) + ((unsigned long) uaddr & ~PAGE_MASK);
+#endif
+
+	*uval = *uaddr;
+
+	ret = cmpxchg(uaddr, oldval, newval);
+
+#ifdef CONFIG_64BIT
+	pagefault_enable();
+#else
+	kunmap_atomic(uaddr);
+#endif
+	ret = 0;
+
+out_inatomic:
+	preempt_enable();
+	return ret;
+}
+EXPORT_SYMBOL(futex_atomic_cmpxchg_inatomic);
diff --git a/arch/um/kernel/stacktrace.c b/arch/um/kernel/stacktrace.c
new file mode 100644
index 000000000..fd3b61b3d
--- /dev/null
+++ b/arch/um/kernel/stacktrace.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright (C) 2013 Richard Weinberger <richard@nod.at>
+ * Copyright (C) 2014 Google Inc., Author: Daniel Walter <dwalter@google.com>
+ */
+
+#include <linux/kallsyms.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/stacktrace.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <asm/stacktrace.h>
+
+void dump_trace(struct task_struct *tsk,
+		const struct stacktrace_ops *ops,
+		void *data)
+{
+	int reliable = 0;
+	unsigned long *sp, bp, addr;
+	struct pt_regs *segv_regs = tsk->thread.segv_regs;
+	struct stack_frame *frame;
+
+	bp = get_frame_pointer(tsk, segv_regs);
+	sp = get_stack_pointer(tsk, segv_regs);
+
+	frame = (struct stack_frame *)bp;
+	while (((long) sp & (THREAD_SIZE-1)) != 0) {
+		addr = READ_ONCE_NOCHECK(*sp);
+		if (__kernel_text_address(addr)) {
+			reliable = 0;
+			if ((unsigned long) sp == bp + sizeof(long)) {
+				frame = frame ? frame->next_frame : NULL;
+				bp = (unsigned long)frame;
+				reliable = 1;
+			}
+			ops->address(data, addr, reliable);
+		}
+		sp++;
+	}
+}
+
+static void save_addr(void *data, unsigned long address, int reliable)
+{
+	struct stack_trace *trace = data;
+
+	if (!reliable)
+		return;
+	if (trace->nr_entries >= trace->max_entries)
+		return;
+
+	trace->entries[trace->nr_entries++] = address;
+}
+
+static const struct stacktrace_ops dump_ops = {
+	.address = save_addr
+};
+
+static void __save_stack_trace(struct task_struct *tsk, struct stack_trace *trace)
+{
+	dump_trace(tsk, &dump_ops, trace);
+}
+
+void save_stack_trace(struct stack_trace *trace)
+{
+	__save_stack_trace(current, trace);
+}
+EXPORT_SYMBOL_GPL(save_stack_trace);
+
+void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
+{
+	__save_stack_trace(tsk, trace);
+}
+EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
diff --git a/arch/um/kernel/sysrq.c b/arch/um/kernel/sysrq.c
new file mode 100644
index 000000000..746715379
--- /dev/null
+++ b/arch/um/kernel/sysrq.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright (C) 2013 Richard Weinberger <richrd@nod.at>
+ */
+
+#include <linux/kallsyms.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/sched/task_stack.h>
+
+#include <asm/sysrq.h>
+#include <asm/stacktrace.h>
+#include <os.h>
+
+static void _print_addr(void *data, unsigned long address, int reliable)
+{
+	const char *loglvl = data;
+
+	printk("%s [<%08lx>] %s%pS\n", loglvl, address, reliable ? "" : "? ",
+		(void *)address);
+}
+
+static const struct stacktrace_ops stackops = {
+	.address = _print_addr
+};
+
+void show_stack(struct task_struct *task, unsigned long *stack,
+		       const char *loglvl)
+{
+	struct pt_regs *segv_regs = current->thread.segv_regs;
+	int i;
+
+	if (!segv_regs && os_is_signal_stack()) {
+		pr_err("Received SIGSEGV in SIGSEGV handler,"
+				" aborting stack trace!\n");
+		return;
+	}
+
+	if (!stack)
+		stack = get_stack_pointer(task, segv_regs);
+
+	printk("%sStack:\n", loglvl);
+	for (i = 0; i < 3 * STACKSLOTS_PER_LINE; i++) {
+		if (kstack_end(stack))
+			break;
+		if (i && ((i % STACKSLOTS_PER_LINE) == 0))
+			pr_cont("\n");
+		pr_cont(" %08lx", READ_ONCE_NOCHECK(*stack));
+		stack++;
+	}
+
+	printk("%sCall Trace:\n", loglvl);
+	dump_trace(current, &stackops, (void *)loglvl);
+}
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
new file mode 100644
index 000000000..fddd1dec2
--- /dev/null
+++ b/arch/um/kernel/time.c
@@ -0,0 +1,860 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2012-2014 Cisco Systems
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright (C) 2019 Intel Corporation
+ */
+
+#include <linux/clockchips.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/jiffies.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/spinlock.h>
+#include <linux/threads.h>
+#include <asm/irq.h>
+#include <asm/param.h>
+#include <kern_util.h>
+#include <os.h>
+#include <linux/time-internal.h>
+#include <linux/um_timetravel.h>
+#include <shared/init.h>
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+enum time_travel_mode time_travel_mode;
+EXPORT_SYMBOL_GPL(time_travel_mode);
+
+static bool time_travel_start_set;
+static unsigned long long time_travel_start;
+static unsigned long long time_travel_time;
+static LIST_HEAD(time_travel_events);
+static LIST_HEAD(time_travel_irqs);
+static unsigned long long time_travel_timer_interval;
+static unsigned long long time_travel_next_event;
+static struct time_travel_event time_travel_timer_event;
+static int time_travel_ext_fd = -1;
+static unsigned int time_travel_ext_waiting;
+static bool time_travel_ext_prev_request_valid;
+static unsigned long long time_travel_ext_prev_request;
+static bool time_travel_ext_free_until_valid;
+static unsigned long long time_travel_ext_free_until;
+
+static void time_travel_set_time(unsigned long long ns)
+{
+	if (unlikely(ns < time_travel_time))
+		panic("time-travel: time goes backwards %lld -> %lld\n",
+		      time_travel_time, ns);
+	else if (unlikely(ns >= S64_MAX))
+		panic("The system was going to sleep forever, aborting");
+
+	time_travel_time = ns;
+}
+
+enum time_travel_message_handling {
+	TTMH_IDLE,
+	TTMH_POLL,
+	TTMH_READ,
+};
+
+static void time_travel_handle_message(struct um_timetravel_msg *msg,
+				       enum time_travel_message_handling mode)
+{
+	struct um_timetravel_msg resp = {
+		.op = UM_TIMETRAVEL_ACK,
+	};
+	int ret;
+
+	/*
+	 * We can't unlock here, but interrupt signals with a timetravel_handler
+	 * (see um_request_irq_tt) get to the timetravel_handler anyway.
+	 */
+	if (mode != TTMH_READ) {
+		BUG_ON(mode == TTMH_IDLE && !irqs_disabled());
+
+		while (os_poll(1, &time_travel_ext_fd) != 0) {
+			/* nothing */
+		}
+	}
+
+	ret = os_read_file(time_travel_ext_fd, msg, sizeof(*msg));
+
+	if (ret == 0)
+		panic("time-travel external link is broken\n");
+	if (ret != sizeof(*msg))
+		panic("invalid time-travel message - %d bytes\n", ret);
+
+	switch (msg->op) {
+	default:
+		WARN_ONCE(1, "time-travel: unexpected message %lld\n",
+			  (unsigned long long)msg->op);
+		break;
+	case UM_TIMETRAVEL_ACK:
+		return;
+	case UM_TIMETRAVEL_RUN:
+		time_travel_set_time(msg->time);
+		break;
+	case UM_TIMETRAVEL_FREE_UNTIL:
+		time_travel_ext_free_until_valid = true;
+		time_travel_ext_free_until = msg->time;
+		break;
+	}
+
+	resp.seq = msg->seq;
+	os_write_file(time_travel_ext_fd, &resp, sizeof(resp));
+}
+
+static u64 time_travel_ext_req(u32 op, u64 time)
+{
+	static int seq;
+	int mseq = ++seq;
+	struct um_timetravel_msg msg = {
+		.op = op,
+		.time = time,
+		.seq = mseq,
+	};
+
+	/*
+	 * We need to block even the timetravel handlers of SIGIO here and
+	 * only restore their use when we got the ACK - otherwise we may
+	 * (will) get interrupted by that, try to queue the IRQ for future
+	 * processing and thus send another request while we're still waiting
+	 * for an ACK, but the peer doesn't know we got interrupted and will
+	 * send the ACKs in the same order as the message, but we'd need to
+	 * see them in the opposite order ...
+	 *
+	 * This wouldn't matter *too* much, but some ACKs carry the
+	 * current time (for UM_TIMETRAVEL_GET) and getting another
+	 * ACK without a time would confuse us a lot!
+	 *
+	 * The sequence number assignment that happens here lets us
+	 * debug such message handling issues more easily.
+	 */
+	block_signals_hard();
+	os_write_file(time_travel_ext_fd, &msg, sizeof(msg));
+
+	while (msg.op != UM_TIMETRAVEL_ACK)
+		time_travel_handle_message(&msg, TTMH_READ);
+
+	if (msg.seq != mseq)
+		panic("time-travel: ACK message has different seqno! op=%d, seq=%d != %d time=%lld\n",
+		      msg.op, msg.seq, mseq, msg.time);
+
+	if (op == UM_TIMETRAVEL_GET)
+		time_travel_set_time(msg.time);
+	unblock_signals_hard();
+
+	return msg.time;
+}
+
+void __time_travel_wait_readable(int fd)
+{
+	int fds[2] = { fd, time_travel_ext_fd };
+	int ret;
+
+	if (time_travel_mode != TT_MODE_EXTERNAL)
+		return;
+
+	while ((ret = os_poll(2, fds))) {
+		struct um_timetravel_msg msg;
+
+		if (ret == 1)
+			time_travel_handle_message(&msg, TTMH_READ);
+	}
+}
+EXPORT_SYMBOL_GPL(__time_travel_wait_readable);
+
+static void time_travel_ext_update_request(unsigned long long time)
+{
+	if (time_travel_mode != TT_MODE_EXTERNAL)
+		return;
+
+	/* asked for exactly this time previously */
+	if (time_travel_ext_prev_request_valid &&
+	    time == time_travel_ext_prev_request)
+		return;
+
+	/*
+	 * if we're running and are allowed to run past the request
+	 * then we don't need to update it either
+	 */
+	if (!time_travel_ext_waiting && time_travel_ext_free_until_valid &&
+	    time < time_travel_ext_free_until)
+		return;
+
+	time_travel_ext_prev_request = time;
+	time_travel_ext_prev_request_valid = true;
+	time_travel_ext_req(UM_TIMETRAVEL_REQUEST, time);
+}
+
+void __time_travel_propagate_time(void)
+{
+	static unsigned long long last_propagated;
+
+	if (last_propagated == time_travel_time)
+		return;
+
+	time_travel_ext_req(UM_TIMETRAVEL_UPDATE, time_travel_time);
+	last_propagated = time_travel_time;
+}
+EXPORT_SYMBOL_GPL(__time_travel_propagate_time);
+
+/* returns true if we must do a wait to the simtime device */
+static bool time_travel_ext_request(unsigned long long time)
+{
+	/*
+	 * If we received an external sync point ("free until") then we
+	 * don't have to request/wait for anything until then, unless
+	 * we're already waiting.
+	 */
+	if (!time_travel_ext_waiting && time_travel_ext_free_until_valid &&
+	    time < time_travel_ext_free_until)
+		return false;
+
+	time_travel_ext_update_request(time);
+	return true;
+}
+
+static void time_travel_ext_wait(bool idle)
+{
+	struct um_timetravel_msg msg = {
+		.op = UM_TIMETRAVEL_ACK,
+	};
+
+	time_travel_ext_prev_request_valid = false;
+	time_travel_ext_free_until_valid = false;
+	time_travel_ext_waiting++;
+
+	time_travel_ext_req(UM_TIMETRAVEL_WAIT, -1);
+
+	/*
+	 * Here we are deep in the idle loop, so we have to break out of the
+	 * kernel abstraction in a sense and implement this in terms of the
+	 * UML system waiting on the VQ interrupt while sleeping, when we get
+	 * the signal it'll call time_travel_ext_vq_notify_done() completing the
+	 * call.
+	 */
+	while (msg.op != UM_TIMETRAVEL_RUN)
+		time_travel_handle_message(&msg, idle ? TTMH_IDLE : TTMH_POLL);
+
+	time_travel_ext_waiting--;
+
+	/* we might request more stuff while polling - reset when we run */
+	time_travel_ext_prev_request_valid = false;
+}
+
+static void time_travel_ext_get_time(void)
+{
+	time_travel_ext_req(UM_TIMETRAVEL_GET, -1);
+}
+
+static void __time_travel_update_time(unsigned long long ns, bool idle)
+{
+	if (time_travel_mode == TT_MODE_EXTERNAL && time_travel_ext_request(ns))
+		time_travel_ext_wait(idle);
+	else
+		time_travel_set_time(ns);
+}
+
+static struct time_travel_event *time_travel_first_event(void)
+{
+	return list_first_entry_or_null(&time_travel_events,
+					struct time_travel_event,
+					list);
+}
+
+static void __time_travel_add_event(struct time_travel_event *e,
+				    unsigned long long time)
+{
+	struct time_travel_event *tmp;
+	bool inserted = false;
+	unsigned long flags;
+
+	if (e->pending)
+		return;
+
+	e->pending = true;
+	e->time = time;
+
+	local_irq_save(flags);
+	list_for_each_entry(tmp, &time_travel_events, list) {
+		/*
+		 * Add the new entry before one with higher time,
+		 * or if they're equal and both on stack, because
+		 * in that case we need to unwind the stack in the
+		 * right order, and the later event (timer sleep
+		 * or such) must be dequeued first.
+		 */
+		if ((tmp->time > e->time) ||
+		    (tmp->time == e->time && tmp->onstack && e->onstack)) {
+			list_add_tail(&e->list, &tmp->list);
+			inserted = true;
+			break;
+		}
+	}
+
+	if (!inserted)
+		list_add_tail(&e->list, &time_travel_events);
+
+	tmp = time_travel_first_event();
+	time_travel_ext_update_request(tmp->time);
+	time_travel_next_event = tmp->time;
+	local_irq_restore(flags);
+}
+
+static void time_travel_add_event(struct time_travel_event *e,
+				  unsigned long long time)
+{
+	if (WARN_ON(!e->fn))
+		return;
+
+	__time_travel_add_event(e, time);
+}
+
+void time_travel_add_event_rel(struct time_travel_event *e,
+			       unsigned long long delay_ns)
+{
+	time_travel_add_event(e, time_travel_time + delay_ns);
+}
+
+void time_travel_periodic_timer(struct time_travel_event *e)
+{
+	time_travel_add_event(&time_travel_timer_event,
+			      time_travel_time + time_travel_timer_interval);
+	deliver_alarm();
+}
+
+void deliver_time_travel_irqs(void)
+{
+	struct time_travel_event *e;
+	unsigned long flags;
+
+	/*
+	 * Don't do anything for most cases. Note that because here we have
+	 * to disable IRQs (and re-enable later) we'll actually recurse at
+	 * the end of the function, so this is strictly necessary.
+	 */
+	if (likely(list_empty(&time_travel_irqs)))
+		return;
+
+	local_irq_save(flags);
+	irq_enter();
+	while ((e = list_first_entry_or_null(&time_travel_irqs,
+					     struct time_travel_event,
+					     list))) {
+		list_del(&e->list);
+		e->pending = false;
+		e->fn(e);
+	}
+	irq_exit();
+	local_irq_restore(flags);
+}
+
+static void time_travel_deliver_event(struct time_travel_event *e)
+{
+	if (e == &time_travel_timer_event) {
+		/*
+		 * deliver_alarm() does the irq_enter/irq_exit
+		 * by itself, so must handle it specially here
+		 */
+		e->fn(e);
+	} else if (irqs_disabled()) {
+		list_add_tail(&e->list, &time_travel_irqs);
+		/*
+		 * set pending again, it was set to false when the
+		 * event was deleted from the original list, but
+		 * now it's still pending until we deliver the IRQ.
+		 */
+		e->pending = true;
+	} else {
+		unsigned long flags;
+
+		local_irq_save(flags);
+		irq_enter();
+		e->fn(e);
+		irq_exit();
+		local_irq_restore(flags);
+	}
+}
+
+bool time_travel_del_event(struct time_travel_event *e)
+{
+	unsigned long flags;
+
+	if (!e->pending)
+		return false;
+	local_irq_save(flags);
+	list_del(&e->list);
+	e->pending = false;
+	local_irq_restore(flags);
+	return true;
+}
+
+static void time_travel_update_time(unsigned long long next, bool idle)
+{
+	struct time_travel_event ne = {
+		.onstack = true,
+	};
+	struct time_travel_event *e;
+	bool finished = idle;
+
+	/* add it without a handler - we deal with that specifically below */
+	__time_travel_add_event(&ne, next);
+
+	do {
+		e = time_travel_first_event();
+
+		BUG_ON(!e);
+		__time_travel_update_time(e->time, idle);
+
+		/* new events may have been inserted while we were waiting */
+		if (e == time_travel_first_event()) {
+			BUG_ON(!time_travel_del_event(e));
+			BUG_ON(time_travel_time != e->time);
+
+			if (e == &ne) {
+				finished = true;
+			} else {
+				if (e->onstack)
+					panic("On-stack event dequeued outside of the stack! time=%lld, event time=%lld, event=%pS\n",
+					      time_travel_time, e->time, e);
+				time_travel_deliver_event(e);
+			}
+		}
+
+		e = time_travel_first_event();
+		if (e)
+			time_travel_ext_update_request(e->time);
+	} while (ne.pending && !finished);
+
+	time_travel_del_event(&ne);
+}
+
+void time_travel_ndelay(unsigned long nsec)
+{
+	time_travel_update_time(time_travel_time + nsec, false);
+}
+EXPORT_SYMBOL(time_travel_ndelay);
+
+void time_travel_add_irq_event(struct time_travel_event *e)
+{
+	BUG_ON(time_travel_mode != TT_MODE_EXTERNAL);
+
+	time_travel_ext_get_time();
+	/*
+	 * We could model interrupt latency here, for now just
+	 * don't have any latency at all and request the exact
+	 * same time (again) to run the interrupt...
+	 */
+	time_travel_add_event(e, time_travel_time);
+}
+EXPORT_SYMBOL_GPL(time_travel_add_irq_event);
+
+static void time_travel_oneshot_timer(struct time_travel_event *e)
+{
+	deliver_alarm();
+}
+
+void time_travel_sleep(void)
+{
+	/*
+	 * Wait "forever" (using S64_MAX because there are some potential
+	 * wrapping issues, especially with the current TT_MODE_EXTERNAL
+	 * controller application.
+	 */
+	unsigned long long next = S64_MAX;
+
+	if (time_travel_mode == TT_MODE_BASIC)
+		os_timer_disable();
+
+	time_travel_update_time(next, true);
+
+	if (time_travel_mode == TT_MODE_BASIC &&
+	    time_travel_timer_event.pending) {
+		if (time_travel_timer_event.fn == time_travel_periodic_timer) {
+			/*
+			 * This is somewhat wrong - we should get the first
+			 * one sooner like the os_timer_one_shot() below...
+			 */
+			os_timer_set_interval(time_travel_timer_interval);
+		} else {
+			os_timer_one_shot(time_travel_timer_event.time - next);
+		}
+	}
+}
+
+static void time_travel_handle_real_alarm(void)
+{
+	time_travel_set_time(time_travel_next_event);
+
+	time_travel_del_event(&time_travel_timer_event);
+
+	if (time_travel_timer_event.fn == time_travel_periodic_timer)
+		time_travel_add_event(&time_travel_timer_event,
+				      time_travel_time +
+				      time_travel_timer_interval);
+}
+
+static void time_travel_set_interval(unsigned long long interval)
+{
+	time_travel_timer_interval = interval;
+}
+
+static int time_travel_connect_external(const char *socket)
+{
+	const char *sep;
+	unsigned long long id = (unsigned long long)-1;
+	int rc;
+
+	if ((sep = strchr(socket, ':'))) {
+		char buf[25] = {};
+		if (sep - socket > sizeof(buf) - 1)
+			goto invalid_number;
+
+		memcpy(buf, socket, sep - socket);
+		if (kstrtoull(buf, 0, &id)) {
+invalid_number:
+			panic("time-travel: invalid external ID in string '%s'\n",
+			      socket);
+			return -EINVAL;
+		}
+
+		socket = sep + 1;
+	}
+
+	rc = os_connect_socket(socket);
+	if (rc < 0) {
+		panic("time-travel: failed to connect to external socket %s\n",
+		      socket);
+		return rc;
+	}
+
+	time_travel_ext_fd = rc;
+
+	time_travel_ext_req(UM_TIMETRAVEL_START, id);
+
+	return 1;
+}
+
+static void time_travel_set_start(void)
+{
+	if (time_travel_start_set)
+		return;
+
+	switch (time_travel_mode) {
+	case TT_MODE_EXTERNAL:
+		time_travel_start = time_travel_ext_req(UM_TIMETRAVEL_GET_TOD, -1);
+		/* controller gave us the *current* time, so adjust by that */
+		time_travel_ext_get_time();
+		time_travel_start -= time_travel_time;
+		break;
+	case TT_MODE_INFCPU:
+	case TT_MODE_BASIC:
+		if (!time_travel_start_set)
+			time_travel_start = os_persistent_clock_emulation();
+		break;
+	case TT_MODE_OFF:
+		/* we just read the host clock with os_persistent_clock_emulation() */
+		break;
+	}
+
+	time_travel_start_set = true;
+}
+#else /* CONFIG_UML_TIME_TRAVEL_SUPPORT */
+#define time_travel_start_set 0
+#define time_travel_start 0
+#define time_travel_time 0
+#define time_travel_ext_waiting 0
+
+static inline void time_travel_update_time(unsigned long long ns, bool retearly)
+{
+}
+
+static inline void time_travel_handle_real_alarm(void)
+{
+}
+
+static void time_travel_set_interval(unsigned long long interval)
+{
+}
+
+static inline void time_travel_set_start(void)
+{
+}
+
+/* fail link if this actually gets used */
+extern u64 time_travel_ext_req(u32 op, u64 time);
+
+/* these are empty macros so the struct/fn need not exist */
+#define time_travel_add_event(e, time) do { } while (0)
+/* externally not usable - redefine here so we can */
+#undef time_travel_del_event
+#define time_travel_del_event(e) do { } while (0)
+#endif
+
+void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
+{
+	unsigned long flags;
+
+	/*
+	 * In basic time-travel mode we still get real interrupts
+	 * (signals) but since we don't read time from the OS, we
+	 * must update the simulated time here to the expiry when
+	 * we get a signal.
+	 * This is not the case in inf-cpu mode, since there we
+	 * never get any real signals from the OS.
+	 */
+	if (time_travel_mode == TT_MODE_BASIC)
+		time_travel_handle_real_alarm();
+
+	local_irq_save(flags);
+	do_IRQ(TIMER_IRQ, regs);
+	local_irq_restore(flags);
+}
+
+static int itimer_shutdown(struct clock_event_device *evt)
+{
+	if (time_travel_mode != TT_MODE_OFF)
+		time_travel_del_event(&time_travel_timer_event);
+
+	if (time_travel_mode != TT_MODE_INFCPU &&
+	    time_travel_mode != TT_MODE_EXTERNAL)
+		os_timer_disable();
+
+	return 0;
+}
+
+static int itimer_set_periodic(struct clock_event_device *evt)
+{
+	unsigned long long interval = NSEC_PER_SEC / HZ;
+
+	if (time_travel_mode != TT_MODE_OFF) {
+		time_travel_del_event(&time_travel_timer_event);
+		time_travel_set_event_fn(&time_travel_timer_event,
+					 time_travel_periodic_timer);
+		time_travel_set_interval(interval);
+		time_travel_add_event(&time_travel_timer_event,
+				      time_travel_time + interval);
+	}
+
+	if (time_travel_mode != TT_MODE_INFCPU &&
+	    time_travel_mode != TT_MODE_EXTERNAL)
+		os_timer_set_interval(interval);
+
+	return 0;
+}
+
+static int itimer_next_event(unsigned long delta,
+			     struct clock_event_device *evt)
+{
+	delta += 1;
+
+	if (time_travel_mode != TT_MODE_OFF) {
+		time_travel_del_event(&time_travel_timer_event);
+		time_travel_set_event_fn(&time_travel_timer_event,
+					 time_travel_oneshot_timer);
+		time_travel_add_event(&time_travel_timer_event,
+				      time_travel_time + delta);
+	}
+
+	if (time_travel_mode != TT_MODE_INFCPU &&
+	    time_travel_mode != TT_MODE_EXTERNAL)
+		return os_timer_one_shot(delta);
+
+	return 0;
+}
+
+static int itimer_one_shot(struct clock_event_device *evt)
+{
+	return itimer_next_event(0, evt);
+}
+
+static struct clock_event_device timer_clockevent = {
+	.name			= "posix-timer",
+	.rating			= 250,
+	.cpumask		= cpu_possible_mask,
+	.features		= CLOCK_EVT_FEAT_PERIODIC |
+				  CLOCK_EVT_FEAT_ONESHOT,
+	.set_state_shutdown	= itimer_shutdown,
+	.set_state_periodic	= itimer_set_periodic,
+	.set_state_oneshot	= itimer_one_shot,
+	.set_next_event		= itimer_next_event,
+	.shift			= 0,
+	.max_delta_ns		= 0xffffffff,
+	.max_delta_ticks	= 0xffffffff,
+	.min_delta_ns		= TIMER_MIN_DELTA,
+	.min_delta_ticks	= TIMER_MIN_DELTA, // microsecond resolution should be enough for anyone, same as 640K RAM
+	.irq			= 0,
+	.mult			= 1,
+};
+
+static irqreturn_t um_timer(int irq, void *dev)
+{
+	if (get_current()->mm != NULL)
+	{
+        /* userspace - relay signal, results in correct userspace timers */
+		os_alarm_process(get_current()->mm->context.id.u.pid);
+	}
+
+	(*timer_clockevent.event_handler)(&timer_clockevent);
+
+	return IRQ_HANDLED;
+}
+
+static u64 timer_read(struct clocksource *cs)
+{
+	if (time_travel_mode != TT_MODE_OFF) {
+		/*
+		 * We make reading the timer cost a bit so that we don't get
+		 * stuck in loops that expect time to move more than the
+		 * exact requested sleep amount, e.g. python's socket server,
+		 * see https://bugs.python.org/issue37026.
+		 *
+		 * However, don't do that when we're in interrupt or such as
+		 * then we might recurse into our own processing, and get to
+		 * even more waiting, and that's not good - it messes up the
+		 * "what do I do next" and onstack event we use to know when
+		 * to return from time_travel_update_time().
+		 */
+		if (!irqs_disabled() && !in_interrupt() && !in_softirq() &&
+		    !time_travel_ext_waiting)
+			time_travel_update_time(time_travel_time +
+						TIMER_MULTIPLIER,
+						false);
+		return time_travel_time / TIMER_MULTIPLIER;
+	}
+
+	return os_nsecs() / TIMER_MULTIPLIER;
+}
+
+static struct clocksource timer_clocksource = {
+	.name		= "timer",
+	.rating		= 300,
+	.read		= timer_read,
+	.mask		= CLOCKSOURCE_MASK(64),
+	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+static void __init um_timer_setup(void)
+{
+	int err;
+
+	err = request_irq(TIMER_IRQ, um_timer, IRQF_TIMER, "hr timer", NULL);
+	if (err != 0)
+		printk(KERN_ERR "register_timer : request_irq failed - "
+		       "errno = %d\n", -err);
+
+	err = os_timer_create();
+	if (err != 0) {
+		printk(KERN_ERR "creation of timer failed - errno = %d\n", -err);
+		return;
+	}
+
+	err = clocksource_register_hz(&timer_clocksource, NSEC_PER_SEC/TIMER_MULTIPLIER);
+	if (err) {
+		printk(KERN_ERR "clocksource_register_hz returned %d\n", err);
+		return;
+	}
+	clockevents_register_device(&timer_clockevent);
+}
+
+void read_persistent_clock64(struct timespec64 *ts)
+{
+	long long nsecs;
+
+	time_travel_set_start();
+
+	if (time_travel_mode != TT_MODE_OFF)
+		nsecs = time_travel_start + time_travel_time;
+	else
+		nsecs = os_persistent_clock_emulation();
+
+	set_normalized_timespec64(ts, nsecs / NSEC_PER_SEC,
+				  nsecs % NSEC_PER_SEC);
+}
+
+void __init time_init(void)
+{
+	timer_set_signal_handler();
+	late_time_init = um_timer_setup;
+}
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+unsigned long calibrate_delay_is_known(void)
+{
+	if (time_travel_mode == TT_MODE_INFCPU ||
+	    time_travel_mode == TT_MODE_EXTERNAL)
+		return 1;
+	return 0;
+}
+
+int setup_time_travel(char *str)
+{
+	if (strcmp(str, "=inf-cpu") == 0) {
+		time_travel_mode = TT_MODE_INFCPU;
+		timer_clockevent.name = "time-travel-timer-infcpu";
+		timer_clocksource.name = "time-travel-clock";
+		return 1;
+	}
+
+	if (strncmp(str, "=ext:", 5) == 0) {
+		time_travel_mode = TT_MODE_EXTERNAL;
+		timer_clockevent.name = "time-travel-timer-external";
+		timer_clocksource.name = "time-travel-clock-external";
+		return time_travel_connect_external(str + 5);
+	}
+
+	if (!*str) {
+		time_travel_mode = TT_MODE_BASIC;
+		timer_clockevent.name = "time-travel-timer";
+		timer_clocksource.name = "time-travel-clock";
+		return 1;
+	}
+
+	return -EINVAL;
+}
+
+__setup("time-travel", setup_time_travel);
+__uml_help(setup_time_travel,
+"time-travel\n"
+"This option just enables basic time travel mode, in which the clock/timers\n"
+"inside the UML instance skip forward when there's nothing to do, rather than\n"
+"waiting for real time to elapse. However, instance CPU speed is limited by\n"
+"the real CPU speed, so e.g. a 10ms timer will always fire after ~10ms wall\n"
+"clock (but quicker when there's nothing to do).\n"
+"\n"
+"time-travel=inf-cpu\n"
+"This enables time travel mode with infinite processing power, in which there\n"
+"are no wall clock timers, and any CPU processing happens - as seen from the\n"
+"guest - instantly. This can be useful for accurate simulation regardless of\n"
+"debug overhead, physical CPU speed, etc. but is somewhat dangerous as it can\n"
+"easily lead to getting stuck (e.g. if anything in the system busy loops).\n"
+"\n"
+"time-travel=ext:[ID:]/path/to/socket\n"
+"This enables time travel mode similar to =inf-cpu, except the system will\n"
+"use the given socket to coordinate with a central scheduler, in order to\n"
+"have more than one system simultaneously be on simulated time. The virtio\n"
+"driver code in UML knows about this so you can also simulate networks and\n"
+"devices using it, assuming the device has the right capabilities.\n"
+"The optional ID is a 64-bit integer that's sent to the central scheduler.\n");
+
+int setup_time_travel_start(char *str)
+{
+	int err;
+
+	err = kstrtoull(str, 0, &time_travel_start);
+	if (err)
+		return err;
+
+	time_travel_start_set = 1;
+	return 1;
+}
+
+__setup("time-travel-start", setup_time_travel_start);
+__uml_help(setup_time_travel_start,
+"time-travel-start=<seconds>\n"
+"Configure the UML instance's wall clock to start at this value rather than\n"
+"the host's wall clock at the time of UML boot.\n");
+#endif
diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c
new file mode 100644
index 000000000..ad449173a
--- /dev/null
+++ b/arch/um/kernel/tlb.c
@@ -0,0 +1,602 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/sched/signal.h>
+
+#include <asm/tlbflush.h>
+#include <as-layout.h>
+#include <mem_user.h>
+#include <os.h>
+#include <skas.h>
+#include <kern_util.h>
+
+struct host_vm_change {
+	struct host_vm_op {
+		enum { NONE, MMAP, MUNMAP, MPROTECT } type;
+		union {
+			struct {
+				unsigned long addr;
+				unsigned long len;
+				unsigned int prot;
+				int fd;
+				__u64 offset;
+			} mmap;
+			struct {
+				unsigned long addr;
+				unsigned long len;
+			} munmap;
+			struct {
+				unsigned long addr;
+				unsigned long len;
+				unsigned int prot;
+			} mprotect;
+		} u;
+	} ops[1];
+	int userspace;
+	int index;
+	struct mm_struct *mm;
+	void *data;
+	int force;
+};
+
+#define INIT_HVC(mm, force, userspace) \
+	((struct host_vm_change) \
+	 { .ops		= { { .type = NONE } },	\
+	   .mm		= mm, \
+       	   .data	= NULL, \
+	   .userspace	= userspace, \
+	   .index	= 0, \
+	   .force	= force })
+
+static void report_enomem(void)
+{
+	printk(KERN_ERR "UML ran out of memory on the host side! "
+			"This can happen due to a memory limitation or "
+			"vm.max_map_count has been reached.\n");
+}
+
+static int do_ops(struct host_vm_change *hvc, int end,
+		  int finished)
+{
+	struct host_vm_op *op;
+	int i, ret = 0;
+
+	for (i = 0; i < end && !ret; i++) {
+		op = &hvc->ops[i];
+		switch (op->type) {
+		case MMAP:
+			if (hvc->userspace)
+				ret = map(&hvc->mm->context.id, op->u.mmap.addr,
+					  op->u.mmap.len, op->u.mmap.prot,
+					  op->u.mmap.fd,
+					  op->u.mmap.offset, finished,
+					  &hvc->data);
+			else
+				map_memory(op->u.mmap.addr, op->u.mmap.offset,
+					   op->u.mmap.len, 1, 1, 1);
+			break;
+		case MUNMAP:
+			if (hvc->userspace)
+				ret = unmap(&hvc->mm->context.id,
+					    op->u.munmap.addr,
+					    op->u.munmap.len, finished,
+					    &hvc->data);
+			else
+				ret = os_unmap_memory(
+					(void *) op->u.munmap.addr,
+						      op->u.munmap.len);
+
+			break;
+		case MPROTECT:
+			if (hvc->userspace)
+				ret = protect(&hvc->mm->context.id,
+					      op->u.mprotect.addr,
+					      op->u.mprotect.len,
+					      op->u.mprotect.prot,
+					      finished, &hvc->data);
+			else
+				ret = os_protect_memory(
+					(void *) op->u.mprotect.addr,
+							op->u.mprotect.len,
+							1, 1, 1);
+			break;
+		default:
+			printk(KERN_ERR "Unknown op type %d in do_ops\n",
+			       op->type);
+			BUG();
+			break;
+		}
+	}
+
+	if (ret == -ENOMEM)
+		report_enomem();
+
+	return ret;
+}
+
+static int add_mmap(unsigned long virt, unsigned long phys, unsigned long len,
+		    unsigned int prot, struct host_vm_change *hvc)
+{
+	__u64 offset;
+	struct host_vm_op *last;
+	int fd = -1, ret = 0;
+
+	if (hvc->userspace)
+		fd = phys_mapping(phys, &offset);
+	else
+		offset = phys;
+	if (hvc->index != 0) {
+		last = &hvc->ops[hvc->index - 1];
+		if ((last->type == MMAP) &&
+		   (last->u.mmap.addr + last->u.mmap.len == virt) &&
+		   (last->u.mmap.prot == prot) && (last->u.mmap.fd == fd) &&
+		   (last->u.mmap.offset + last->u.mmap.len == offset)) {
+			last->u.mmap.len += len;
+			return 0;
+		}
+	}
+
+	if (hvc->index == ARRAY_SIZE(hvc->ops)) {
+		ret = do_ops(hvc, ARRAY_SIZE(hvc->ops), 0);
+		hvc->index = 0;
+	}
+
+	hvc->ops[hvc->index++] = ((struct host_vm_op)
+				  { .type	= MMAP,
+				    .u = { .mmap = { .addr	= virt,
+						     .len	= len,
+						     .prot	= prot,
+						     .fd	= fd,
+						     .offset	= offset }
+			   } });
+	return ret;
+}
+
+static int add_munmap(unsigned long addr, unsigned long len,
+		      struct host_vm_change *hvc)
+{
+	struct host_vm_op *last;
+	int ret = 0;
+
+	if (hvc->index != 0) {
+		last = &hvc->ops[hvc->index - 1];
+		if ((last->type == MUNMAP) &&
+		   (last->u.munmap.addr + last->u.mmap.len == addr)) {
+			last->u.munmap.len += len;
+			return 0;
+		}
+	}
+
+	if (hvc->index == ARRAY_SIZE(hvc->ops)) {
+		ret = do_ops(hvc, ARRAY_SIZE(hvc->ops), 0);
+		hvc->index = 0;
+	}
+
+	hvc->ops[hvc->index++] = ((struct host_vm_op)
+				  { .type	= MUNMAP,
+			     	    .u = { .munmap = { .addr	= addr,
+						       .len	= len } } });
+	return ret;
+}
+
+static int add_mprotect(unsigned long addr, unsigned long len,
+			unsigned int prot, struct host_vm_change *hvc)
+{
+	struct host_vm_op *last;
+	int ret = 0;
+
+	if (hvc->index != 0) {
+		last = &hvc->ops[hvc->index - 1];
+		if ((last->type == MPROTECT) &&
+		   (last->u.mprotect.addr + last->u.mprotect.len == addr) &&
+		   (last->u.mprotect.prot == prot)) {
+			last->u.mprotect.len += len;
+			return 0;
+		}
+	}
+
+	if (hvc->index == ARRAY_SIZE(hvc->ops)) {
+		ret = do_ops(hvc, ARRAY_SIZE(hvc->ops), 0);
+		hvc->index = 0;
+	}
+
+	hvc->ops[hvc->index++] = ((struct host_vm_op)
+				  { .type	= MPROTECT,
+			     	    .u = { .mprotect = { .addr	= addr,
+							 .len	= len,
+							 .prot	= prot } } });
+	return ret;
+}
+
+#define ADD_ROUND(n, inc) (((n) + (inc)) & ~((inc) - 1))
+
+static inline int update_pte_range(pmd_t *pmd, unsigned long addr,
+				   unsigned long end,
+				   struct host_vm_change *hvc)
+{
+	pte_t *pte;
+	int r, w, x, prot, ret = 0;
+
+	pte = pte_offset_kernel(pmd, addr);
+	do {
+		r = pte_read(*pte);
+		w = pte_write(*pte);
+		x = pte_exec(*pte);
+		if (!pte_young(*pte)) {
+			r = 0;
+			w = 0;
+		} else if (!pte_dirty(*pte))
+			w = 0;
+
+		prot = ((r ? UM_PROT_READ : 0) | (w ? UM_PROT_WRITE : 0) |
+			(x ? UM_PROT_EXEC : 0));
+		if (hvc->force || pte_newpage(*pte)) {
+			if (pte_present(*pte)) {
+				if (pte_newpage(*pte))
+					ret = add_mmap(addr, pte_val(*pte) & PAGE_MASK,
+						       PAGE_SIZE, prot, hvc);
+			} else
+				ret = add_munmap(addr, PAGE_SIZE, hvc);
+		} else if (pte_newprot(*pte))
+			ret = add_mprotect(addr, PAGE_SIZE, prot, hvc);
+		*pte = pte_mkuptodate(*pte);
+	} while (pte++, addr += PAGE_SIZE, ((addr < end) && !ret));
+	return ret;
+}
+
+static inline int update_pmd_range(pud_t *pud, unsigned long addr,
+				   unsigned long end,
+				   struct host_vm_change *hvc)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	int ret = 0;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (!pmd_present(*pmd)) {
+			if (hvc->force || pmd_newpage(*pmd)) {
+				ret = add_munmap(addr, next - addr, hvc);
+				pmd_mkuptodate(*pmd);
+			}
+		}
+		else ret = update_pte_range(pmd, addr, next, hvc);
+	} while (pmd++, addr = next, ((addr < end) && !ret));
+	return ret;
+}
+
+static inline int update_pud_range(p4d_t *p4d, unsigned long addr,
+				   unsigned long end,
+				   struct host_vm_change *hvc)
+{
+	pud_t *pud;
+	unsigned long next;
+	int ret = 0;
+
+	pud = pud_offset(p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (!pud_present(*pud)) {
+			if (hvc->force || pud_newpage(*pud)) {
+				ret = add_munmap(addr, next - addr, hvc);
+				pud_mkuptodate(*pud);
+			}
+		}
+		else ret = update_pmd_range(pud, addr, next, hvc);
+	} while (pud++, addr = next, ((addr < end) && !ret));
+	return ret;
+}
+
+static inline int update_p4d_range(pgd_t *pgd, unsigned long addr,
+				   unsigned long end,
+				   struct host_vm_change *hvc)
+{
+	p4d_t *p4d;
+	unsigned long next;
+	int ret = 0;
+
+	p4d = p4d_offset(pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		if (!p4d_present(*p4d)) {
+			if (hvc->force || p4d_newpage(*p4d)) {
+				ret = add_munmap(addr, next - addr, hvc);
+				p4d_mkuptodate(*p4d);
+			}
+		} else
+			ret = update_pud_range(p4d, addr, next, hvc);
+	} while (p4d++, addr = next, ((addr < end) && !ret));
+	return ret;
+}
+
+void fix_range_common(struct mm_struct *mm, unsigned long start_addr,
+		      unsigned long end_addr, int force)
+{
+	pgd_t *pgd;
+	struct host_vm_change hvc;
+	unsigned long addr = start_addr, next;
+	int ret = 0, userspace = 1;
+
+	hvc = INIT_HVC(mm, force, userspace);
+	pgd = pgd_offset(mm, addr);
+	do {
+		next = pgd_addr_end(addr, end_addr);
+		if (!pgd_present(*pgd)) {
+			if (force || pgd_newpage(*pgd)) {
+				ret = add_munmap(addr, next - addr, &hvc);
+				pgd_mkuptodate(*pgd);
+			}
+		} else
+			ret = update_p4d_range(pgd, addr, next, &hvc);
+	} while (pgd++, addr = next, ((addr < end_addr) && !ret));
+
+	if (!ret)
+		ret = do_ops(&hvc, hvc.index, 1);
+
+	/* This is not an else because ret is modified above */
+	if (ret) {
+		struct mm_id *mm_idp = &current->mm->context.id;
+
+		printk(KERN_ERR "fix_range_common: failed, killing current "
+		       "process: %d\n", task_tgid_vnr(current));
+		mm_idp->kill = 1;
+	}
+}
+
+static int flush_tlb_kernel_range_common(unsigned long start, unsigned long end)
+{
+	struct mm_struct *mm;
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+	unsigned long addr, last;
+	int updated = 0, err = 0, force = 0, userspace = 0;
+	struct host_vm_change hvc;
+
+	mm = &init_mm;
+	hvc = INIT_HVC(mm, force, userspace);
+	for (addr = start; addr < end;) {
+		pgd = pgd_offset(mm, addr);
+		if (!pgd_present(*pgd)) {
+			last = ADD_ROUND(addr, PGDIR_SIZE);
+			if (last > end)
+				last = end;
+			if (pgd_newpage(*pgd)) {
+				updated = 1;
+				err = add_munmap(addr, last - addr, &hvc);
+				if (err < 0)
+					panic("munmap failed, errno = %d\n",
+					      -err);
+			}
+			addr = last;
+			continue;
+		}
+
+		p4d = p4d_offset(pgd, addr);
+		if (!p4d_present(*p4d)) {
+			last = ADD_ROUND(addr, P4D_SIZE);
+			if (last > end)
+				last = end;
+			if (p4d_newpage(*p4d)) {
+				updated = 1;
+				err = add_munmap(addr, last - addr, &hvc);
+				if (err < 0)
+					panic("munmap failed, errno = %d\n",
+					      -err);
+			}
+			addr = last;
+			continue;
+		}
+
+		pud = pud_offset(p4d, addr);
+		if (!pud_present(*pud)) {
+			last = ADD_ROUND(addr, PUD_SIZE);
+			if (last > end)
+				last = end;
+			if (pud_newpage(*pud)) {
+				updated = 1;
+				err = add_munmap(addr, last - addr, &hvc);
+				if (err < 0)
+					panic("munmap failed, errno = %d\n",
+					      -err);
+			}
+			addr = last;
+			continue;
+		}
+
+		pmd = pmd_offset(pud, addr);
+		if (!pmd_present(*pmd)) {
+			last = ADD_ROUND(addr, PMD_SIZE);
+			if (last > end)
+				last = end;
+			if (pmd_newpage(*pmd)) {
+				updated = 1;
+				err = add_munmap(addr, last - addr, &hvc);
+				if (err < 0)
+					panic("munmap failed, errno = %d\n",
+					      -err);
+			}
+			addr = last;
+			continue;
+		}
+
+		pte = pte_offset_kernel(pmd, addr);
+		if (!pte_present(*pte) || pte_newpage(*pte)) {
+			updated = 1;
+			err = add_munmap(addr, PAGE_SIZE, &hvc);
+			if (err < 0)
+				panic("munmap failed, errno = %d\n",
+				      -err);
+			if (pte_present(*pte))
+				err = add_mmap(addr, pte_val(*pte) & PAGE_MASK,
+					       PAGE_SIZE, 0, &hvc);
+		}
+		else if (pte_newprot(*pte)) {
+			updated = 1;
+			err = add_mprotect(addr, PAGE_SIZE, 0, &hvc);
+		}
+		addr += PAGE_SIZE;
+	}
+	if (!err)
+		err = do_ops(&hvc, hvc.index, 1);
+
+	if (err < 0)
+		panic("flush_tlb_kernel failed, errno = %d\n", err);
+	return updated;
+}
+
+void flush_tlb_page(struct vm_area_struct *vma, unsigned long address)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+	struct mm_struct *mm = vma->vm_mm;
+	void *flush = NULL;
+	int r, w, x, prot, err = 0;
+	struct mm_id *mm_id;
+
+	address &= PAGE_MASK;
+
+	pgd = pgd_offset(mm, address);
+	if (!pgd_present(*pgd))
+		goto kill;
+
+	p4d = p4d_offset(pgd, address);
+	if (!p4d_present(*p4d))
+		goto kill;
+
+	pud = pud_offset(p4d, address);
+	if (!pud_present(*pud))
+		goto kill;
+
+	pmd = pmd_offset(pud, address);
+	if (!pmd_present(*pmd))
+		goto kill;
+
+	pte = pte_offset_kernel(pmd, address);
+
+	r = pte_read(*pte);
+	w = pte_write(*pte);
+	x = pte_exec(*pte);
+	if (!pte_young(*pte)) {
+		r = 0;
+		w = 0;
+	} else if (!pte_dirty(*pte)) {
+		w = 0;
+	}
+
+	mm_id = &mm->context.id;
+	prot = ((r ? UM_PROT_READ : 0) | (w ? UM_PROT_WRITE : 0) |
+		(x ? UM_PROT_EXEC : 0));
+	if (pte_newpage(*pte)) {
+		if (pte_present(*pte)) {
+			unsigned long long offset;
+			int fd;
+
+			fd = phys_mapping(pte_val(*pte) & PAGE_MASK, &offset);
+			err = map(mm_id, address, PAGE_SIZE, prot, fd, offset,
+				  1, &flush);
+		}
+		else err = unmap(mm_id, address, PAGE_SIZE, 1, &flush);
+	}
+	else if (pte_newprot(*pte))
+		err = protect(mm_id, address, PAGE_SIZE, prot, 1, &flush);
+
+	if (err) {
+		if (err == -ENOMEM)
+			report_enomem();
+
+		goto kill;
+	}
+
+	*pte = pte_mkuptodate(*pte);
+
+	return;
+
+kill:
+	printk(KERN_ERR "Failed to flush page for address 0x%lx\n", address);
+	force_sig(SIGKILL);
+}
+
+void flush_tlb_all(void)
+{
+	/*
+	 * Don't bother flushing if this address space is about to be
+	 * destroyed.
+	 */
+	if (atomic_read(&current->mm->mm_users) == 0)
+		return;
+
+	flush_tlb_mm(current->mm);
+}
+
+void flush_tlb_kernel_range(unsigned long start, unsigned long end)
+{
+	flush_tlb_kernel_range_common(start, end);
+}
+
+void flush_tlb_kernel_vm(void)
+{
+	flush_tlb_kernel_range_common(start_vm, end_vm);
+}
+
+void __flush_tlb_one(unsigned long addr)
+{
+	flush_tlb_kernel_range_common(addr, addr + PAGE_SIZE);
+}
+
+static void fix_range(struct mm_struct *mm, unsigned long start_addr,
+		      unsigned long end_addr, int force)
+{
+	/*
+	 * Don't bother flushing if this address space is about to be
+	 * destroyed.
+	 */
+	if (atomic_read(&mm->mm_users) == 0)
+		return;
+
+	fix_range_common(mm, start_addr, end_addr, force);
+}
+
+void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
+		     unsigned long end)
+{
+	if (vma->vm_mm == NULL)
+		flush_tlb_kernel_range_common(start, end);
+	else fix_range(vma->vm_mm, start, end, 0);
+}
+EXPORT_SYMBOL(flush_tlb_range);
+
+void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
+			unsigned long end)
+{
+	fix_range(mm, start, end, 0);
+}
+
+void flush_tlb_mm(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+	VMA_ITERATOR(vmi, mm, 0);
+
+	for_each_vma(vmi, vma)
+		fix_range(mm, vma->vm_start, vma->vm_end, 0);
+}
+
+void force_flush_all(void)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+	VMA_ITERATOR(vmi, mm, 0);
+
+	for_each_vma(vmi, vma)
+		fix_range(mm, vma->vm_start, vma->vm_end, 1);
+}
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
new file mode 100644
index 000000000..6d8ae86ae
--- /dev/null
+++ b/arch/um/kernel/trap.c
@@ -0,0 +1,315 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/hardirq.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/sched/debug.h>
+#include <asm/current.h>
+#include <asm/tlbflush.h>
+#include <arch.h>
+#include <as-layout.h>
+#include <kern_util.h>
+#include <os.h>
+#include <skas.h>
+
+/*
+ * Note this is constrained to return 0, -EFAULT, -EACCES, -ENOMEM by
+ * segv().
+ */
+int handle_page_fault(unsigned long address, unsigned long ip,
+		      int is_write, int is_user, int *code_out)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+	pmd_t *pmd;
+	pte_t *pte;
+	int err = -EFAULT;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
+
+	*code_out = SEGV_MAPERR;
+
+	/*
+	 * If the fault was with pagefaults disabled, don't take the fault, just
+	 * fail.
+	 */
+	if (faulthandler_disabled())
+		goto out_nosemaphore;
+
+	if (is_user)
+		flags |= FAULT_FLAG_USER;
+retry:
+	mmap_read_lock(mm);
+	vma = find_vma(mm, address);
+	if (!vma)
+		goto out;
+	if (vma->vm_start <= address)
+		goto good_area;
+	if (!(vma->vm_flags & VM_GROWSDOWN))
+		goto out;
+	if (is_user && !ARCH_IS_STACKGROW(address))
+		goto out;
+	vma = expand_stack(mm, address);
+	if (!vma)
+		goto out_nosemaphore;
+
+good_area:
+	*code_out = SEGV_ACCERR;
+	if (is_write) {
+		if (!(vma->vm_flags & VM_WRITE))
+			goto out;
+		flags |= FAULT_FLAG_WRITE;
+	} else {
+		/* Don't require VM_READ|VM_EXEC for write faults! */
+		if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
+			goto out;
+	}
+
+	do {
+		vm_fault_t fault;
+
+		fault = handle_mm_fault(vma, address, flags, NULL);
+
+		if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+			goto out_nosemaphore;
+
+		/* The fault is fully completed (including releasing mmap lock) */
+		if (fault & VM_FAULT_COMPLETED)
+			return 0;
+
+		if (unlikely(fault & VM_FAULT_ERROR)) {
+			if (fault & VM_FAULT_OOM) {
+				goto out_of_memory;
+			} else if (fault & VM_FAULT_SIGSEGV) {
+				goto out;
+			} else if (fault & VM_FAULT_SIGBUS) {
+				err = -EACCES;
+				goto out;
+			}
+			BUG();
+		}
+		if (fault & VM_FAULT_RETRY) {
+			flags |= FAULT_FLAG_TRIED;
+
+			goto retry;
+		}
+
+		pmd = pmd_off(mm, address);
+		pte = pte_offset_kernel(pmd, address);
+	} while (!pte_present(*pte));
+	err = 0;
+	/*
+	 * The below warning was added in place of
+	 *	pte_mkyoung(); if (is_write) pte_mkdirty();
+	 * If it's triggered, we'd see normally a hang here (a clean pte is
+	 * marked read-only to emulate the dirty bit).
+	 * However, the generic code can mark a PTE writable but clean on a
+	 * concurrent read fault, triggering this harmlessly. So comment it out.
+	 */
+#if 0
+	WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
+#endif
+	flush_tlb_page(vma, address);
+out:
+	mmap_read_unlock(mm);
+out_nosemaphore:
+	return err;
+
+out_of_memory:
+	/*
+	 * We ran out of memory, call the OOM killer, and return the userspace
+	 * (which will retry the fault, or kill us if we got oom-killed).
+	 */
+	mmap_read_unlock(mm);
+	if (!is_user)
+		goto out_nosemaphore;
+	pagefault_out_of_memory();
+	return 0;
+}
+
+static void show_segv_info(struct uml_pt_regs *regs)
+{
+	struct task_struct *tsk = current;
+	struct faultinfo *fi = UPT_FAULTINFO(regs);
+
+	if (!unhandled_signal(tsk, SIGSEGV))
+		return;
+
+	if (!printk_ratelimit())
+		return;
+
+	printk("%s%s[%d]: segfault at %lx ip %px sp %px error %x",
+		task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
+		tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
+		(void *)UPT_IP(regs), (void *)UPT_SP(regs),
+		fi->error_code);
+
+	print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
+	printk(KERN_CONT "\n");
+}
+
+static void bad_segv(struct faultinfo fi, unsigned long ip)
+{
+	current->thread.arch.faultinfo = fi;
+	force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi));
+}
+
+void fatal_sigsegv(void)
+{
+	force_fatal_sig(SIGSEGV);
+	do_signal(&current->thread.regs);
+	/*
+	 * This is to tell gcc that we're not returning - do_signal
+	 * can, in general, return, but in this case, it's not, since
+	 * we just got a fatal SIGSEGV queued.
+	 */
+	os_dump_core();
+}
+
+/**
+ * segv_handler() - the SIGSEGV handler
+ * @sig:	the signal number
+ * @unused_si:	the signal info struct; unused in this handler
+ * @regs:	the ptrace register information
+ *
+ * The handler first extracts the faultinfo from the UML ptrace regs struct.
+ * If the userfault did not happen in an UML userspace process, bad_segv is called.
+ * Otherwise the signal did happen in a cloned userspace process, handle it.
+ */
+void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
+{
+	struct faultinfo * fi = UPT_FAULTINFO(regs);
+
+	if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
+		show_segv_info(regs);
+		bad_segv(*fi, UPT_IP(regs));
+		return;
+	}
+	segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
+}
+
+/*
+ * We give a *copy* of the faultinfo in the regs to segv.
+ * This must be done, since nesting SEGVs could overwrite
+ * the info in the regs. A pointer to the info then would
+ * give us bad data!
+ */
+unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
+		   struct uml_pt_regs *regs)
+{
+	jmp_buf *catcher;
+	int si_code;
+	int err;
+	int is_write = FAULT_WRITE(fi);
+	unsigned long address = FAULT_ADDRESS(fi);
+
+	if (!is_user && regs)
+		current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
+
+	if (!is_user && (address >= start_vm) && (address < end_vm)) {
+		flush_tlb_kernel_vm();
+		goto out;
+	}
+	else if (current->mm == NULL) {
+		show_regs(container_of(regs, struct pt_regs, regs));
+		panic("Segfault with no mm");
+	}
+	else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
+		show_regs(container_of(regs, struct pt_regs, regs));
+		panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
+		       address, ip);
+	}
+
+	if (SEGV_IS_FIXABLE(&fi))
+		err = handle_page_fault(address, ip, is_write, is_user,
+					&si_code);
+	else {
+		err = -EFAULT;
+		/*
+		 * A thread accessed NULL, we get a fault, but CR2 is invalid.
+		 * This code is used in __do_copy_from_user() of TT mode.
+		 * XXX tt mode is gone, so maybe this isn't needed any more
+		 */
+		address = 0;
+	}
+
+	catcher = current->thread.fault_catcher;
+	if (!err)
+		goto out;
+	else if (catcher != NULL) {
+		current->thread.fault_addr = (void *) address;
+		UML_LONGJMP(catcher, 1);
+	}
+	else if (current->thread.fault_addr != NULL)
+		panic("fault_addr set but no fault catcher");
+	else if (!is_user && arch_fixup(ip, regs))
+		goto out;
+
+	if (!is_user) {
+		show_regs(container_of(regs, struct pt_regs, regs));
+		panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
+		      address, ip);
+	}
+
+	show_segv_info(regs);
+
+	if (err == -EACCES) {
+		current->thread.arch.faultinfo = fi;
+		force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
+	} else {
+		BUG_ON(err != -EFAULT);
+		current->thread.arch.faultinfo = fi;
+		force_sig_fault(SIGSEGV, si_code, (void __user *) address);
+	}
+
+out:
+	if (regs)
+		current->thread.segv_regs = NULL;
+
+	return 0;
+}
+
+void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
+{
+	int code, err;
+	if (!UPT_IS_USER(regs)) {
+		if (sig == SIGBUS)
+			printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
+			       "mount likely just ran out of space\n");
+		panic("Kernel mode signal %d", sig);
+	}
+
+	arch_examine_signal(sig, regs);
+
+	/* Is the signal layout for the signal known?
+	 * Signal data must be scrubbed to prevent information leaks.
+	 */
+	code = si->si_code;
+	err = si->si_errno;
+	if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) {
+		struct faultinfo *fi = UPT_FAULTINFO(regs);
+		current->thread.arch.faultinfo = *fi;
+		force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi));
+	} else {
+		printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d) with errno %d\n",
+		       sig, code, err);
+		force_sig(sig);
+	}
+}
+
+void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs)
+{
+	if (current->thread.fault_catcher != NULL)
+		UML_LONGJMP(current->thread.fault_catcher, 1);
+	else
+		relay_signal(sig, si, regs);
+}
+
+void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
+{
+	do_IRQ(WINCH_IRQ, regs);
+}
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
new file mode 100644
index 000000000..334c91191
--- /dev/null
+++ b/arch/um/kernel/um_arch.c
@@ -0,0 +1,532 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/cpu.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/ctype.h>
+#include <linux/module.h>
+#include <linux/panic_notifier.h>
+#include <linux/seq_file.h>
+#include <linux/string.h>
+#include <linux/utsname.h>
+#include <linux/sched.h>
+#include <linux/sched/task.h>
+#include <linux/kmsg_dump.h>
+#include <linux/suspend.h>
+#include <linux/random.h>
+
+#include <asm/processor.h>
+#include <asm/cpufeature.h>
+#include <asm/sections.h>
+#include <asm/setup.h>
+#include <as-layout.h>
+#include <arch.h>
+#include <init.h>
+#include <kern.h>
+#include <kern_util.h>
+#include <mem_user.h>
+#include <os.h>
+
+#include "um_arch.h"
+
+#define DEFAULT_COMMAND_LINE_ROOT "root=98:0"
+#define DEFAULT_COMMAND_LINE_CONSOLE "console=tty0"
+
+/* Changed in add_arg and setup_arch, which run before SMP is started */
+static char __initdata command_line[COMMAND_LINE_SIZE] = { 0 };
+
+static void __init add_arg(char *arg)
+{
+	if (strlen(command_line) + strlen(arg) + 1 > COMMAND_LINE_SIZE) {
+		os_warn("add_arg: Too many command line arguments!\n");
+		exit(1);
+	}
+	if (strlen(command_line) > 0)
+		strcat(command_line, " ");
+	strcat(command_line, arg);
+}
+
+/*
+ * These fields are initialized at boot time and not changed.
+ * XXX This structure is used only in the non-SMP case.  Maybe this
+ * should be moved to smp.c.
+ */
+struct cpuinfo_um boot_cpu_data = {
+	.loops_per_jiffy	= 0,
+	.ipi_pipe		= { -1, -1 },
+	.cache_alignment	= L1_CACHE_BYTES,
+	.x86_capability		= { 0 }
+};
+
+EXPORT_SYMBOL(boot_cpu_data);
+
+union thread_union cpu0_irqstack
+	__section(".data..init_irqstack") =
+		{ .thread_info = INIT_THREAD_INFO(init_task) };
+
+/* Changed in setup_arch, which is called in early boot */
+static char host_info[(__NEW_UTS_LEN + 1) * 5];
+
+static int show_cpuinfo(struct seq_file *m, void *v)
+{
+	int i = 0;
+
+	seq_printf(m, "processor\t: %d\n", i);
+	seq_printf(m, "vendor_id\t: User Mode Linux\n");
+	seq_printf(m, "model name\t: UML\n");
+	seq_printf(m, "mode\t\t: skas\n");
+	seq_printf(m, "host\t\t: %s\n", host_info);
+	seq_printf(m, "fpu\t\t: %s\n", cpu_has(&boot_cpu_data, X86_FEATURE_FPU) ? "yes" : "no");
+	seq_printf(m, "flags\t\t:");
+	for (i = 0; i < 32*NCAPINTS; i++)
+		if (cpu_has(&boot_cpu_data, i) && (x86_cap_flags[i] != NULL))
+			seq_printf(m, " %s", x86_cap_flags[i]);
+	seq_printf(m, "\n");
+	seq_printf(m, "cache_alignment\t: %d\n", boot_cpu_data.cache_alignment);
+	seq_printf(m, "bogomips\t: %lu.%02lu\n",
+		   loops_per_jiffy/(500000/HZ),
+		   (loops_per_jiffy/(5000/HZ)) % 100);
+
+
+	return 0;
+}
+
+static void *c_start(struct seq_file *m, loff_t *pos)
+{
+	return *pos < nr_cpu_ids ? cpu_data + *pos : NULL;
+}
+
+static void *c_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	++*pos;
+	return c_start(m, pos);
+}
+
+static void c_stop(struct seq_file *m, void *v)
+{
+}
+
+const struct seq_operations cpuinfo_op = {
+	.start	= c_start,
+	.next	= c_next,
+	.stop	= c_stop,
+	.show	= show_cpuinfo,
+};
+
+/* Set in linux_main */
+unsigned long uml_physmem;
+EXPORT_SYMBOL(uml_physmem);
+
+unsigned long uml_reserved; /* Also modified in mem_init */
+unsigned long start_vm;
+unsigned long end_vm;
+
+/* Set in uml_ncpus_setup */
+int ncpus = 1;
+
+/* Set in early boot */
+static int have_root __initdata;
+static int have_console __initdata;
+
+/* Set in uml_mem_setup and modified in linux_main */
+long long physmem_size = 64 * 1024 * 1024;
+EXPORT_SYMBOL(physmem_size);
+
+static const char *usage_string =
+"User Mode Linux v%s\n"
+"	available at http://user-mode-linux.sourceforge.net/\n\n";
+
+static int __init uml_version_setup(char *line, int *add)
+{
+	/* Explicitly use printf() to show version in stdout */
+	printf("%s\n", init_utsname()->release);
+	exit(0);
+
+	return 0;
+}
+
+__uml_setup("--version", uml_version_setup,
+"--version\n"
+"    Prints the version number of the kernel.\n\n"
+);
+
+static int __init uml_root_setup(char *line, int *add)
+{
+	have_root = 1;
+	return 0;
+}
+
+__uml_setup("root=", uml_root_setup,
+"root=<file containing the root fs>\n"
+"    This is actually used by the generic kernel in exactly the same\n"
+"    way as in any other kernel. If you configure a number of block\n"
+"    devices and want to boot off something other than ubd0, you \n"
+"    would use something like:\n"
+"        root=/dev/ubd5\n\n"
+);
+
+static int __init no_skas_debug_setup(char *line, int *add)
+{
+	os_warn("'debug' is not necessary to gdb UML in skas mode - run\n");
+	os_warn("'gdb linux'\n");
+
+	return 0;
+}
+
+__uml_setup("debug", no_skas_debug_setup,
+"debug\n"
+"    this flag is not needed to run gdb on UML in skas mode\n\n"
+);
+
+static int __init uml_console_setup(char *line, int *add)
+{
+	have_console = 1;
+	return 0;
+}
+
+__uml_setup("console=", uml_console_setup,
+"console=<preferred console>\n"
+"    Specify the preferred console output driver\n\n"
+);
+
+static int __init Usage(char *line, int *add)
+{
+	const char **p;
+
+	printf(usage_string, init_utsname()->release);
+	p = &__uml_help_start;
+	/* Explicitly use printf() to show help in stdout */
+	while (p < &__uml_help_end) {
+		printf("%s", *p);
+		p++;
+	}
+	exit(0);
+	return 0;
+}
+
+__uml_setup("--help", Usage,
+"--help\n"
+"    Prints this message.\n\n"
+);
+
+static void __init uml_checksetup(char *line, int *add)
+{
+	struct uml_param *p;
+
+	p = &__uml_setup_start;
+	while (p < &__uml_setup_end) {
+		size_t n;
+
+		n = strlen(p->str);
+		if (!strncmp(line, p->str, n) && p->setup_func(line + n, add))
+			return;
+		p++;
+	}
+}
+
+static void __init uml_postsetup(void)
+{
+	initcall_t *p;
+
+	p = &__uml_postsetup_start;
+	while (p < &__uml_postsetup_end) {
+		(*p)();
+		p++;
+	}
+	return;
+}
+
+static int panic_exit(struct notifier_block *self, unsigned long unused1,
+		      void *unused2)
+{
+	kmsg_dump(KMSG_DUMP_PANIC);
+	bust_spinlocks(1);
+	bust_spinlocks(0);
+	uml_exitcode = 1;
+	os_dump_core();
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block panic_exit_notifier = {
+	.notifier_call	= panic_exit,
+	.priority	= INT_MAX - 1, /* run as 2nd notifier, won't return */
+};
+
+void uml_finishsetup(void)
+{
+	atomic_notifier_chain_register(&panic_notifier_list,
+				       &panic_exit_notifier);
+
+	uml_postsetup();
+
+	new_thread_handler();
+}
+
+/* Set during early boot */
+unsigned long stub_start;
+unsigned long task_size;
+EXPORT_SYMBOL(task_size);
+
+unsigned long host_task_size;
+
+unsigned long brk_start;
+unsigned long end_iomem;
+EXPORT_SYMBOL(end_iomem);
+
+#define MIN_VMALLOC (32 * 1024 * 1024)
+
+static void parse_host_cpu_flags(char *line)
+{
+	int i;
+	for (i = 0; i < 32*NCAPINTS; i++) {
+		if ((x86_cap_flags[i] != NULL) && strstr(line, x86_cap_flags[i]))
+			set_cpu_cap(&boot_cpu_data, i);
+	}
+}
+static void parse_cache_line(char *line)
+{
+	long res;
+	char *to_parse = strstr(line, ":");
+	if (to_parse) {
+		to_parse++;
+		while (*to_parse != 0 && isspace(*to_parse)) {
+			to_parse++;
+		}
+		if (kstrtoul(to_parse, 10, &res) == 0 && is_power_of_2(res))
+			boot_cpu_data.cache_alignment = res;
+		else
+			boot_cpu_data.cache_alignment = L1_CACHE_BYTES;
+	}
+}
+
+int __init linux_main(int argc, char **argv)
+{
+	unsigned long avail, diff;
+	unsigned long virtmem_size, max_physmem;
+	unsigned long stack;
+	unsigned int i;
+	int add;
+
+	for (i = 1; i < argc; i++) {
+		if ((i == 1) && (argv[i][0] == ' '))
+			continue;
+		add = 1;
+		uml_checksetup(argv[i], &add);
+		if (add)
+			add_arg(argv[i]);
+	}
+	if (have_root == 0)
+		add_arg(DEFAULT_COMMAND_LINE_ROOT);
+
+	if (have_console == 0)
+		add_arg(DEFAULT_COMMAND_LINE_CONSOLE);
+
+	host_task_size = os_get_top_address();
+	/* reserve two pages for the stubs */
+	host_task_size -= 2 * PAGE_SIZE;
+	stub_start = host_task_size;
+
+	/*
+	 * TASK_SIZE needs to be PGDIR_SIZE aligned or else exit_mmap craps
+	 * out
+	 */
+	task_size = host_task_size & PGDIR_MASK;
+
+	/* OS sanity checks that need to happen before the kernel runs */
+	os_early_checks();
+
+	get_host_cpu_features(parse_host_cpu_flags, parse_cache_line);
+
+	brk_start = (unsigned long) sbrk(0);
+
+	/*
+	 * Increase physical memory size for exec-shield users
+	 * so they actually get what they asked for. This should
+	 * add zero for non-exec shield users
+	 */
+
+	diff = UML_ROUND_UP(brk_start) - UML_ROUND_UP(&_end);
+	if (diff > 1024 * 1024) {
+		os_info("Adding %ld bytes to physical memory to account for "
+			"exec-shield gap\n", diff);
+		physmem_size += UML_ROUND_UP(brk_start) - UML_ROUND_UP(&_end);
+	}
+
+	uml_physmem = (unsigned long) __binary_start & PAGE_MASK;
+
+	/* Reserve up to 4M after the current brk */
+	uml_reserved = ROUND_4M(brk_start) + (1 << 22);
+
+	setup_machinename(init_utsname()->machine);
+
+	highmem = 0;
+	iomem_size = (iomem_size + PAGE_SIZE - 1) & PAGE_MASK;
+	max_physmem = TASK_SIZE - uml_physmem - iomem_size - MIN_VMALLOC;
+
+	/*
+	 * Zones have to begin on a 1 << MAX_ORDER page boundary,
+	 * so this makes sure that's true for highmem
+	 */
+	max_physmem &= ~((1 << (PAGE_SHIFT + MAX_ORDER)) - 1);
+	if (physmem_size + iomem_size > max_physmem) {
+		highmem = physmem_size + iomem_size - max_physmem;
+		physmem_size -= highmem;
+	}
+
+	high_physmem = uml_physmem + physmem_size;
+	end_iomem = high_physmem + iomem_size;
+	high_memory = (void *) end_iomem;
+
+	start_vm = VMALLOC_START;
+
+	virtmem_size = physmem_size;
+	stack = (unsigned long) argv;
+	stack &= ~(1024 * 1024 - 1);
+	avail = stack - start_vm;
+	if (physmem_size > avail)
+		virtmem_size = avail;
+	end_vm = start_vm + virtmem_size;
+
+	if (virtmem_size < physmem_size)
+		os_info("Kernel virtual memory size shrunk to %lu bytes\n",
+			virtmem_size);
+
+	os_flush_stdout();
+
+	return start_uml();
+}
+
+int __init __weak read_initrd(void)
+{
+	return 0;
+}
+
+void __init setup_arch(char **cmdline_p)
+{
+	u8 rng_seed[32];
+
+	stack_protections((unsigned long) &init_thread_info);
+	setup_physmem(uml_physmem, uml_reserved, physmem_size, highmem);
+	mem_total_pages(physmem_size, iomem_size, highmem);
+	uml_dtb_init();
+	read_initrd();
+
+	paging_init();
+	strscpy(boot_command_line, command_line, COMMAND_LINE_SIZE);
+	*cmdline_p = command_line;
+	setup_hostinfo(host_info, sizeof host_info);
+
+	if (os_getrandom(rng_seed, sizeof(rng_seed), 0) == sizeof(rng_seed)) {
+		add_bootloader_randomness(rng_seed, sizeof(rng_seed));
+		memzero_explicit(rng_seed, sizeof(rng_seed));
+	}
+}
+
+void __init arch_cpu_finalize_init(void)
+{
+	arch_check_bugs();
+	os_check_bugs();
+}
+
+void apply_ibt_endbr(s32 *start, s32 *end)
+{
+}
+
+void apply_retpolines(s32 *start, s32 *end)
+{
+}
+
+void apply_returns(s32 *start, s32 *end)
+{
+}
+
+void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
+{
+}
+
+void *text_poke(void *addr, const void *opcode, size_t len)
+{
+	/*
+	 * In UML, the only reference to this function is in
+	 * apply_relocate_add(), which shouldn't ever actually call this
+	 * because UML doesn't have live patching.
+	 */
+	WARN_ON(1);
+
+	return memcpy(addr, opcode, len);
+}
+
+void text_poke_sync(void)
+{
+}
+
+void uml_pm_wake(void)
+{
+	pm_system_wakeup();
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int um_suspend_valid(suspend_state_t state)
+{
+	return state == PM_SUSPEND_MEM;
+}
+
+static int um_suspend_prepare(void)
+{
+	um_irqs_suspend();
+	return 0;
+}
+
+static int um_suspend_enter(suspend_state_t state)
+{
+	if (WARN_ON(state != PM_SUSPEND_MEM))
+		return -EINVAL;
+
+	/*
+	 * This is identical to the idle sleep, but we've just
+	 * (during suspend) turned off all interrupt sources
+	 * except for the ones we want, so now we can only wake
+	 * up on something we actually want to wake up on. All
+	 * timing has also been suspended.
+	 */
+	um_idle_sleep();
+	return 0;
+}
+
+static void um_suspend_finish(void)
+{
+	um_irqs_resume();
+}
+
+const struct platform_suspend_ops um_suspend_ops = {
+	.valid = um_suspend_valid,
+	.prepare = um_suspend_prepare,
+	.enter = um_suspend_enter,
+	.finish = um_suspend_finish,
+};
+
+static int init_pm_wake_signal(void)
+{
+	/*
+	 * In external time-travel mode we can't use signals to wake up
+	 * since that would mess with the scheduling. We'll have to do
+	 * some additional work to support wakeup on virtio devices or
+	 * similar, perhaps implementing a fake RTC controller that can
+	 * trigger wakeup (and request the appropriate scheduling from
+	 * the external scheduler when going to suspend.)
+	 */
+	if (time_travel_mode != TT_MODE_EXTERNAL)
+		register_pm_wake_signal();
+
+	suspend_set_ops(&um_suspend_ops);
+
+	return 0;
+}
+
+late_initcall(init_pm_wake_signal);
+#endif
diff --git a/arch/um/kernel/um_arch.h b/arch/um/kernel/um_arch.h
new file mode 100644
index 000000000..1e07fb7ee
--- /dev/null
+++ b/arch/um/kernel/um_arch.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __UML_ARCH_H__
+#define __UML_ARCH_H__
+
+extern void * __init uml_load_file(const char *filename, unsigned long long *size);
+
+#ifdef CONFIG_OF
+extern void __init uml_dtb_init(void);
+#else
+static inline void uml_dtb_init(void) { }
+#endif
+
+#endif
diff --git a/arch/um/kernel/umid.c b/arch/um/kernel/umid.c
new file mode 100644
index 000000000..72bc60ade
--- /dev/null
+++ b/arch/um/kernel/umid.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <asm/errno.h>
+#include <init.h>
+#include <kern.h>
+#include <os.h>
+
+/* Changed by set_umid_arg */
+static int umid_inited;
+
+static int __init set_umid_arg(char *name, int *add)
+{
+	int err;
+
+	if (umid_inited) {
+		os_warn("umid already set\n");
+		return 0;
+	}
+
+	*add = 0;
+	err = set_umid(name);
+	if (err == -EEXIST)
+		os_warn("umid '%s' already in use\n", name);
+	else if (!err)
+		umid_inited = 1;
+
+	return 0;
+}
+
+__uml_setup("umid=", set_umid_arg,
+"umid=<name>\n"
+"    This is used to assign a unique identity to this UML machine and\n"
+"    is used for naming the pid file and management console socket.\n\n"
+);
+
diff --git a/arch/um/kernel/uml.lds.S b/arch/um/kernel/uml.lds.S
new file mode 100644
index 000000000..71a59b8ad
--- /dev/null
+++ b/arch/um/kernel/uml.lds.S
@@ -0,0 +1,122 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <asm/vmlinux.lds.h>
+#include <asm/page.h>
+
+OUTPUT_FORMAT(ELF_FORMAT)
+OUTPUT_ARCH(ELF_ARCH)
+ENTRY(_start)
+jiffies = jiffies_64;
+
+VERSION {
+  {
+    local: *;
+  };
+}
+
+SECTIONS
+{
+  /* This must contain the right address - not quite the default ELF one.*/
+  PROVIDE (__executable_start = START);
+  /* Static binaries stick stuff here, like the sigreturn trampoline,
+   * invisibly to objdump.  So, just make __binary_start equal to the very
+   * beginning of the executable, and if there are unmapped pages after this,
+   * they are forever unusable.
+   */
+  __binary_start = START;
+
+  . = START + SIZEOF_HEADERS;
+  . = ALIGN(PAGE_SIZE);
+
+  _text = .;
+  INIT_TEXT_SECTION(0)
+
+  .text      :
+  {
+    _stext = .;
+    TEXT_TEXT
+    SCHED_TEXT
+    CPUIDLE_TEXT
+    LOCK_TEXT
+    IRQENTRY_TEXT
+    SOFTIRQENTRY_TEXT
+    *(.fixup)
+    /* .gnu.warning sections are handled specially by elf32.em.  */
+    *(.gnu.warning)
+    *(.gnu.linkonce.t*)
+  }
+
+  . = ALIGN(PAGE_SIZE);
+  .syscall_stub : {
+	__syscall_stub_start = .;
+	*(.__syscall_stub*)
+	__syscall_stub_end = .;
+  }
+
+  /*
+   * These are needed even in a static link, even if they wind up being empty.
+   * Newer glibc needs these __rel{,a}_iplt_{start,end} symbols.
+   */
+  .rel.plt : {
+	*(.rel.plt)
+	PROVIDE_HIDDEN(__rel_iplt_start = .);
+	*(.rel.iplt)
+	PROVIDE_HIDDEN(__rel_iplt_end = .);
+  }
+  .rela.plt : {
+	*(.rela.plt)
+	PROVIDE_HIDDEN(__rela_iplt_start = .);
+	*(.rela.iplt)
+	PROVIDE_HIDDEN(__rela_iplt_end = .);
+  }
+
+  #include <asm/common.lds.S>
+
+  __init_begin = .;
+  init.data : { INIT_DATA }
+  __init_end = .;
+
+  .data    :
+  {
+    INIT_TASK_DATA(KERNEL_STACK_SIZE)
+    . = ALIGN(KERNEL_STACK_SIZE);
+    *(.data..init_irqstack)
+    DATA_DATA
+    *(.gnu.linkonce.d*)
+    CONSTRUCTORS
+  }
+  .data1   : { *(.data1) }
+  .ctors         :
+  {
+    *(.ctors)
+  }
+  .dtors         :
+  {
+    *(.dtors)
+  }
+
+  .got           : { *(.got.plt) *(.got) }
+  .eh_frame       : { KEEP (*(.eh_frame)) }
+  .dynamic       : { *(.dynamic) }
+  .tdata	  : { *(.tdata .tdata.* .gnu.linkonce.td.*) }
+  .tbss		  : { *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon) }
+  /* We want the small data sections together, so single-instruction offsets
+     can access them all, and initialized data all before uninitialized, so
+     we can shorten the on-disk segment size.  */
+  .sdata     : { *(.sdata) }
+  _edata  =  .;
+  PROVIDE (edata = .);
+  . = ALIGN(PAGE_SIZE);
+  __bss_start = .;
+  PROVIDE(_bss_start = .);
+  SBSS(0)
+  BSS(0)
+   __bss_stop = .;
+  _end = .;
+  PROVIDE (end = .);
+
+  STABS_DEBUG
+  DWARF_DEBUG
+  ELF_DETAILS
+
+  DISCARDS
+}
diff --git a/arch/um/kernel/vmlinux.lds.S b/arch/um/kernel/vmlinux.lds.S
new file mode 100644
index 000000000..53d719c04
--- /dev/null
+++ b/arch/um/kernel/vmlinux.lds.S
@@ -0,0 +1,8 @@
+#define RUNTIME_DISCARD_EXIT
+KERNEL_STACK_SIZE = 4096 * (1 << CONFIG_KERNEL_STACK_ORDER);
+
+#ifdef CONFIG_LD_SCRIPT_STATIC
+#include "uml.lds.S"
+#else
+#include "dyn.lds.S"
+#endif