Adding upstream version 4.19.249.upstream/4.19.249

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

1 files changed, 837 insertions, 0 deletions

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
new file mode 100644
index 000000000..a6e3c7022
--- /dev/null
+++ b/arch/s390/mm/fault.c
@@ -0,0 +1,837 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  S390 version
+ *    Copyright IBM Corp. 1999
+ *    Author(s): Hartmut Penner (hp@de.ibm.com)
+ *               Ulrich Weigand (uweigand@de.ibm.com)
+ *
+ *  Derived from "arch/i386/mm/fault.c"
+ *    Copyright (C) 1995  Linus Torvalds
+ */
+
+#include <linux/kernel_stat.h>
+#include <linux/perf_event.h>
+#include <linux/signal.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/ptrace.h>
+#include <linux/mman.h>
+#include <linux/mm.h>
+#include <linux/compat.h>
+#include <linux/smp.h>
+#include <linux/kdebug.h>
+#include <linux/init.h>
+#include <linux/console.h>
+#include <linux/extable.h>
+#include <linux/hardirq.h>
+#include <linux/kprobes.h>
+#include <linux/uaccess.h>
+#include <linux/hugetlb.h>
+#include <asm/asm-offsets.h>
+#include <asm/diag.h>
+#include <asm/pgtable.h>
+#include <asm/gmap.h>
+#include <asm/irq.h>
+#include <asm/mmu_context.h>
+#include <asm/facility.h>
+#include "../kernel/entry.h"
+
+#define __FAIL_ADDR_MASK -4096L
+#define __SUBCODE_MASK 0x0600
+#define __PF_RES_FIELD 0x8000000000000000ULL
+
+#define VM_FAULT_BADCONTEXT	0x010000
+#define VM_FAULT_BADMAP		0x020000
+#define VM_FAULT_BADACCESS	0x040000
+#define VM_FAULT_SIGNAL		0x080000
+#define VM_FAULT_PFAULT		0x100000
+
+enum fault_type {
+	KERNEL_FAULT,
+	USER_FAULT,
+	VDSO_FAULT,
+	GMAP_FAULT,
+};
+
+static unsigned long store_indication __read_mostly;
+
+static int __init fault_init(void)
+{
+	if (test_facility(75))
+		store_indication = 0xc00;
+	return 0;
+}
+early_initcall(fault_init);
+
+static inline int notify_page_fault(struct pt_regs *regs)
+{
+	int ret = 0;
+
+	/* kprobe_running() needs smp_processor_id() */
+	if (kprobes_built_in() && !user_mode(regs)) {
+		preempt_disable();
+		if (kprobe_running() && kprobe_fault_handler(regs, 14))
+			ret = 1;
+		preempt_enable();
+	}
+	return ret;
+}
+
+
+/*
+ * Unlock any spinlocks which will prevent us from getting the
+ * message out.
+ */
+void bust_spinlocks(int yes)
+{
+	if (yes) {
+		oops_in_progress = 1;
+	} else {
+		int loglevel_save = console_loglevel;
+		console_unblank();
+		oops_in_progress = 0;
+		/*
+		 * OK, the message is on the console.  Now we call printk()
+		 * without oops_in_progress set so that printk will give klogd
+		 * a poke.  Hold onto your hats...
+		 */
+		console_loglevel = 15;
+		printk(" ");
+		console_loglevel = loglevel_save;
+	}
+}
+
+/*
+ * Find out which address space caused the exception.
+ */
+static inline enum fault_type get_fault_type(struct pt_regs *regs)
+{
+	unsigned long trans_exc_code;
+
+	trans_exc_code = regs->int_parm_long & 3;
+	if (likely(trans_exc_code == 0)) {
+		/* primary space exception */
+		if (IS_ENABLED(CONFIG_PGSTE) &&
+		    test_pt_regs_flag(regs, PIF_GUEST_FAULT))
+			return GMAP_FAULT;
+		if (current->thread.mm_segment == USER_DS)
+			return USER_FAULT;
+		return KERNEL_FAULT;
+	}
+	if (trans_exc_code == 2) {
+		/* secondary space exception */
+		if (current->thread.mm_segment & 1) {
+			if (current->thread.mm_segment == USER_DS_SACF)
+				return USER_FAULT;
+			return KERNEL_FAULT;
+		}
+		return VDSO_FAULT;
+	}
+	if (trans_exc_code == 1) {
+		/* access register mode, not used in the kernel */
+		return USER_FAULT;
+	}
+	/* home space exception -> access via kernel ASCE */
+	return KERNEL_FAULT;
+}
+
+static int bad_address(void *p)
+{
+	unsigned long dummy;
+
+	return probe_kernel_address((unsigned long *)p, dummy);
+}
+
+static void dump_pagetable(unsigned long asce, unsigned long address)
+{
+	unsigned long *table = __va(asce & _ASCE_ORIGIN);
+
+	pr_alert("AS:%016lx ", asce);
+	switch (asce & _ASCE_TYPE_MASK) {
+	case _ASCE_TYPE_REGION1:
+		table += (address & _REGION1_INDEX) >> _REGION1_SHIFT;
+		if (bad_address(table))
+			goto bad;
+		pr_cont("R1:%016lx ", *table);
+		if (*table & _REGION_ENTRY_INVALID)
+			goto out;
+		table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
+		/* fallthrough */
+	case _ASCE_TYPE_REGION2:
+		table += (address & _REGION2_INDEX) >> _REGION2_SHIFT;
+		if (bad_address(table))
+			goto bad;
+		pr_cont("R2:%016lx ", *table);
+		if (*table & _REGION_ENTRY_INVALID)
+			goto out;
+		table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
+		/* fallthrough */
+	case _ASCE_TYPE_REGION3:
+		table += (address & _REGION3_INDEX) >> _REGION3_SHIFT;
+		if (bad_address(table))
+			goto bad;
+		pr_cont("R3:%016lx ", *table);
+		if (*table & (_REGION_ENTRY_INVALID | _REGION3_ENTRY_LARGE))
+			goto out;
+		table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
+		/* fallthrough */
+	case _ASCE_TYPE_SEGMENT:
+		table += (address & _SEGMENT_INDEX) >> _SEGMENT_SHIFT;
+		if (bad_address(table))
+			goto bad;
+		pr_cont("S:%016lx ", *table);
+		if (*table & (_SEGMENT_ENTRY_INVALID | _SEGMENT_ENTRY_LARGE))
+			goto out;
+		table = (unsigned long *)(*table & _SEGMENT_ENTRY_ORIGIN);
+	}
+	table += (address & _PAGE_INDEX) >> _PAGE_SHIFT;
+	if (bad_address(table))
+		goto bad;
+	pr_cont("P:%016lx ", *table);
+out:
+	pr_cont("\n");
+	return;
+bad:
+	pr_cont("BAD\n");
+}
+
+static void dump_fault_info(struct pt_regs *regs)
+{
+	unsigned long asce;
+
+	pr_alert("Failing address: %016lx TEID: %016lx\n",
+		 regs->int_parm_long & __FAIL_ADDR_MASK, regs->int_parm_long);
+	pr_alert("Fault in ");
+	switch (regs->int_parm_long & 3) {
+	case 3:
+		pr_cont("home space ");
+		break;
+	case 2:
+		pr_cont("secondary space ");
+		break;
+	case 1:
+		pr_cont("access register ");
+		break;
+	case 0:
+		pr_cont("primary space ");
+		break;
+	}
+	pr_cont("mode while using ");
+	switch (get_fault_type(regs)) {
+	case USER_FAULT:
+		asce = S390_lowcore.user_asce;
+		pr_cont("user ");
+		break;
+	case VDSO_FAULT:
+		asce = S390_lowcore.vdso_asce;
+		pr_cont("vdso ");
+		break;
+	case GMAP_FAULT:
+		asce = ((struct gmap *) S390_lowcore.gmap)->asce;
+		pr_cont("gmap ");
+		break;
+	case KERNEL_FAULT:
+		asce = S390_lowcore.kernel_asce;
+		pr_cont("kernel ");
+		break;
+	}
+	pr_cont("ASCE.\n");
+	dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);
+}
+
+int show_unhandled_signals = 1;
+
+void report_user_fault(struct pt_regs *regs, long signr, int is_mm_fault)
+{
+	if ((task_pid_nr(current) > 1) && !show_unhandled_signals)
+		return;
+	if (!unhandled_signal(current, signr))
+		return;
+	if (!printk_ratelimit())
+		return;
+	printk(KERN_ALERT "User process fault: interruption code %04x ilc:%d ",
+	       regs->int_code & 0xffff, regs->int_code >> 17);
+	print_vma_addr(KERN_CONT "in ", regs->psw.addr);
+	printk(KERN_CONT "\n");
+	if (is_mm_fault)
+		dump_fault_info(regs);
+	show_regs(regs);
+}
+
+/*
+ * Send SIGSEGV to task.  This is an external routine
+ * to keep the stack usage of do_page_fault small.
+ */
+static noinline void do_sigsegv(struct pt_regs *regs, int si_code)
+{
+	report_user_fault(regs, SIGSEGV, 1);
+	force_sig_fault(SIGSEGV, si_code,
+			(void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK),
+			current);
+}
+
+static noinline void do_no_context(struct pt_regs *regs)
+{
+	const struct exception_table_entry *fixup;
+
+	/* Are we prepared to handle this kernel fault?  */
+	fixup = search_exception_tables(regs->psw.addr);
+	if (fixup) {
+		regs->psw.addr = extable_fixup(fixup);
+		return;
+	}
+
+	/*
+	 * Oops. The kernel tried to access some bad page. We'll have to
+	 * terminate things with extreme prejudice.
+	 */
+	if (get_fault_type(regs) == KERNEL_FAULT)
+		printk(KERN_ALERT "Unable to handle kernel pointer dereference"
+		       " in virtual kernel address space\n");
+	else
+		printk(KERN_ALERT "Unable to handle kernel paging request"
+		       " in virtual user address space\n");
+	dump_fault_info(regs);
+	die(regs, "Oops");
+	do_exit(SIGKILL);
+}
+
+static noinline void do_low_address(struct pt_regs *regs)
+{
+	/* Low-address protection hit in kernel mode means
+	   NULL pointer write access in kernel mode.  */
+	if (regs->psw.mask & PSW_MASK_PSTATE) {
+		/* Low-address protection hit in user mode 'cannot happen'. */
+		die (regs, "Low-address protection");
+		do_exit(SIGKILL);
+	}
+
+	do_no_context(regs);
+}
+
+static noinline void do_sigbus(struct pt_regs *regs)
+{
+	/*
+	 * Send a sigbus, regardless of whether we were in kernel
+	 * or user mode.
+	 */
+	force_sig_fault(SIGBUS, BUS_ADRERR,
+			(void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK),
+			current);
+}
+
+static noinline int signal_return(struct pt_regs *regs)
+{
+	u16 instruction;
+	int rc;
+
+	rc = __get_user(instruction, (u16 __user *) regs->psw.addr);
+	if (rc)
+		return rc;
+	if (instruction == 0x0a77) {
+		set_pt_regs_flag(regs, PIF_SYSCALL);
+		regs->int_code = 0x00040077;
+		return 0;
+	} else if (instruction == 0x0aad) {
+		set_pt_regs_flag(regs, PIF_SYSCALL);
+		regs->int_code = 0x000400ad;
+		return 0;
+	}
+	return -EACCES;
+}
+
+static noinline void do_fault_error(struct pt_regs *regs, int access,
+					vm_fault_t fault)
+{
+	int si_code;
+
+	switch (fault) {
+	case VM_FAULT_BADACCESS:
+		if (access == VM_EXEC && signal_return(regs) == 0)
+			break;
+	case VM_FAULT_BADMAP:
+		/* Bad memory access. Check if it is kernel or user space. */
+		if (user_mode(regs)) {
+			/* User mode accesses just cause a SIGSEGV */
+			si_code = (fault == VM_FAULT_BADMAP) ?
+				SEGV_MAPERR : SEGV_ACCERR;
+			do_sigsegv(regs, si_code);
+			break;
+		}
+	case VM_FAULT_BADCONTEXT:
+	case VM_FAULT_PFAULT:
+		do_no_context(regs);
+		break;
+	case VM_FAULT_SIGNAL:
+		if (!user_mode(regs))
+			do_no_context(regs);
+		break;
+	default: /* fault & VM_FAULT_ERROR */
+		if (fault & VM_FAULT_OOM) {
+			if (!user_mode(regs))
+				do_no_context(regs);
+			else
+				pagefault_out_of_memory();
+		} else if (fault & VM_FAULT_SIGSEGV) {
+			/* Kernel mode? Handle exceptions or die */
+			if (!user_mode(regs))
+				do_no_context(regs);
+			else
+				do_sigsegv(regs, SEGV_MAPERR);
+		} else if (fault & VM_FAULT_SIGBUS) {
+			/* Kernel mode? Handle exceptions or die */
+			if (!user_mode(regs))
+				do_no_context(regs);
+			else
+				do_sigbus(regs);
+		} else
+			BUG();
+		break;
+	}
+}
+
+/*
+ * This routine handles page faults.  It determines the address,
+ * and the problem, and then passes it off to one of the appropriate
+ * routines.
+ *
+ * interruption code (int_code):
+ *   04       Protection           ->  Write-Protection  (suprression)
+ *   10       Segment translation  ->  Not present       (nullification)
+ *   11       Page translation     ->  Not present       (nullification)
+ *   3b       Region third trans.  ->  Not present       (nullification)
+ */
+static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
+{
+	struct gmap *gmap;
+	struct task_struct *tsk;
+	struct mm_struct *mm;
+	struct vm_area_struct *vma;
+	enum fault_type type;
+	unsigned long trans_exc_code;
+	unsigned long address;
+	unsigned int flags;
+	vm_fault_t fault;
+
+	tsk = current;
+	/*
+	 * The instruction that caused the program check has
+	 * been nullified. Don't signal single step via SIGTRAP.
+	 */
+	clear_pt_regs_flag(regs, PIF_PER_TRAP);
+
+	if (notify_page_fault(regs))
+		return 0;
+
+	mm = tsk->mm;
+	trans_exc_code = regs->int_parm_long;
+
+	/*
+	 * Verify that the fault happened in user space, that
+	 * we are not in an interrupt and that there is a 
+	 * user context.
+	 */
+	fault = VM_FAULT_BADCONTEXT;
+	type = get_fault_type(regs);
+	switch (type) {
+	case KERNEL_FAULT:
+		goto out;
+	case VDSO_FAULT:
+		fault = VM_FAULT_BADMAP;
+		goto out;
+	case USER_FAULT:
+	case GMAP_FAULT:
+		if (faulthandler_disabled() || !mm)
+			goto out;
+		break;
+	}
+
+	address = trans_exc_code & __FAIL_ADDR_MASK;
+	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
+	flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	if (user_mode(regs))
+		flags |= FAULT_FLAG_USER;
+	if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
+		flags |= FAULT_FLAG_WRITE;
+	down_read(&mm->mmap_sem);
+
+	gmap = NULL;
+	if (IS_ENABLED(CONFIG_PGSTE) && type == GMAP_FAULT) {
+		gmap = (struct gmap *) S390_lowcore.gmap;
+		current->thread.gmap_addr = address;
+		current->thread.gmap_write_flag = !!(flags & FAULT_FLAG_WRITE);
+		current->thread.gmap_int_code = regs->int_code & 0xffff;
+		address = __gmap_translate(gmap, address);
+		if (address == -EFAULT) {
+			fault = VM_FAULT_BADMAP;
+			goto out_up;
+		}
+		if (gmap->pfault_enabled)
+			flags |= FAULT_FLAG_RETRY_NOWAIT;
+	}
+
+retry:
+	fault = VM_FAULT_BADMAP;
+	vma = find_vma(mm, address);
+	if (!vma)
+		goto out_up;
+
+	if (unlikely(vma->vm_start > address)) {
+		if (!(vma->vm_flags & VM_GROWSDOWN))
+			goto out_up;
+		if (expand_stack(vma, address))
+			goto out_up;
+	}
+
+	/*
+	 * Ok, we have a good vm_area for this memory access, so
+	 * we can handle it..
+	 */
+	fault = VM_FAULT_BADACCESS;
+	if (unlikely(!(vma->vm_flags & access)))
+		goto out_up;
+
+	if (is_vm_hugetlb_page(vma))
+		address &= HPAGE_MASK;
+	/*
+	 * If for any reason at all we couldn't handle the fault,
+	 * make sure we exit gracefully rather than endlessly redo
+	 * the fault.
+	 */
+	fault = handle_mm_fault(vma, address, flags);
+	/* No reason to continue if interrupted by SIGKILL. */
+	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
+		fault = VM_FAULT_SIGNAL;
+		if (flags & FAULT_FLAG_RETRY_NOWAIT)
+			goto out_up;
+		goto out;
+	}
+	if (unlikely(fault & VM_FAULT_ERROR))
+		goto out_up;
+
+	/*
+	 * Major/minor page fault accounting is only done on the
+	 * initial attempt. If we go through a retry, it is extremely
+	 * likely that the page will be found in page cache at that point.
+	 */
+	if (flags & FAULT_FLAG_ALLOW_RETRY) {
+		if (fault & VM_FAULT_MAJOR) {
+			tsk->maj_flt++;
+			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
+				      regs, address);
+		} else {
+			tsk->min_flt++;
+			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
+				      regs, address);
+		}
+		if (fault & VM_FAULT_RETRY) {
+			if (IS_ENABLED(CONFIG_PGSTE) && gmap &&
+			    (flags & FAULT_FLAG_RETRY_NOWAIT)) {
+				/* FAULT_FLAG_RETRY_NOWAIT has been set,
+				 * mmap_sem has not been released */
+				current->thread.gmap_pfault = 1;
+				fault = VM_FAULT_PFAULT;
+				goto out_up;
+			}
+			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
+			 * of starvation. */
+			flags &= ~(FAULT_FLAG_ALLOW_RETRY |
+				   FAULT_FLAG_RETRY_NOWAIT);
+			flags |= FAULT_FLAG_TRIED;
+			down_read(&mm->mmap_sem);
+			goto retry;
+		}
+	}
+	if (IS_ENABLED(CONFIG_PGSTE) && gmap) {
+		address =  __gmap_link(gmap, current->thread.gmap_addr,
+				       address);
+		if (address == -EFAULT) {
+			fault = VM_FAULT_BADMAP;
+			goto out_up;
+		}
+		if (address == -ENOMEM) {
+			fault = VM_FAULT_OOM;
+			goto out_up;
+		}
+	}
+	fault = 0;
+out_up:
+	up_read(&mm->mmap_sem);
+out:
+	return fault;
+}
+
+void do_protection_exception(struct pt_regs *regs)
+{
+	unsigned long trans_exc_code;
+	int access;
+	vm_fault_t fault;
+
+	trans_exc_code = regs->int_parm_long;
+	/*
+	 * Protection exceptions are suppressing, decrement psw address.
+	 * The exception to this rule are aborted transactions, for these
+	 * the PSW already points to the correct location.
+	 */
+	if (!(regs->int_code & 0x200))
+		regs->psw.addr = __rewind_psw(regs->psw, regs->int_code >> 16);
+	/*
+	 * Check for low-address protection.  This needs to be treated
+	 * as a special case because the translation exception code
+	 * field is not guaranteed to contain valid data in this case.
+	 */
+	if (unlikely(!(trans_exc_code & 4))) {
+		do_low_address(regs);
+		return;
+	}
+	if (unlikely(MACHINE_HAS_NX && (trans_exc_code & 0x80))) {
+		regs->int_parm_long = (trans_exc_code & ~PAGE_MASK) |
+					(regs->psw.addr & PAGE_MASK);
+		access = VM_EXEC;
+		fault = VM_FAULT_BADACCESS;
+	} else {
+		access = VM_WRITE;
+		fault = do_exception(regs, access);
+	}
+	if (unlikely(fault))
+		do_fault_error(regs, access, fault);
+}
+NOKPROBE_SYMBOL(do_protection_exception);
+
+void do_dat_exception(struct pt_regs *regs)
+{
+	int access;
+	vm_fault_t fault;
+
+	access = VM_READ | VM_EXEC | VM_WRITE;
+	fault = do_exception(regs, access);
+	if (unlikely(fault))
+		do_fault_error(regs, access, fault);
+}
+NOKPROBE_SYMBOL(do_dat_exception);
+
+#ifdef CONFIG_PFAULT 
+/*
+ * 'pfault' pseudo page faults routines.
+ */
+static int pfault_disable;
+
+static int __init nopfault(char *str)
+{
+	pfault_disable = 1;
+	return 1;
+}
+
+__setup("nopfault", nopfault);
+
+struct pfault_refbk {
+	u16 refdiagc;
+	u16 reffcode;
+	u16 refdwlen;
+	u16 refversn;
+	u64 refgaddr;
+	u64 refselmk;
+	u64 refcmpmk;
+	u64 reserved;
+} __attribute__ ((packed, aligned(8)));
+
+int pfault_init(void)
+{
+	struct pfault_refbk refbk = {
+		.refdiagc = 0x258,
+		.reffcode = 0,
+		.refdwlen = 5,
+		.refversn = 2,
+		.refgaddr = __LC_LPP,
+		.refselmk = 1ULL << 48,
+		.refcmpmk = 1ULL << 48,
+		.reserved = __PF_RES_FIELD };
+        int rc;
+
+	if (pfault_disable)
+		return -1;
+	diag_stat_inc(DIAG_STAT_X258);
+	asm volatile(
+		"	diag	%1,%0,0x258\n"
+		"0:	j	2f\n"
+		"1:	la	%0,8\n"
+		"2:\n"
+		EX_TABLE(0b,1b)
+		: "=d" (rc) : "a" (&refbk), "m" (refbk) : "cc");
+        return rc;
+}
+
+void pfault_fini(void)
+{
+	struct pfault_refbk refbk = {
+		.refdiagc = 0x258,
+		.reffcode = 1,
+		.refdwlen = 5,
+		.refversn = 2,
+	};
+
+	if (pfault_disable)
+		return;
+	diag_stat_inc(DIAG_STAT_X258);
+	asm volatile(
+		"	diag	%0,0,0x258\n"
+		"0:	nopr	%%r7\n"
+		EX_TABLE(0b,0b)
+		: : "a" (&refbk), "m" (refbk) : "cc");
+}
+
+static DEFINE_SPINLOCK(pfault_lock);
+static LIST_HEAD(pfault_list);
+
+#define PF_COMPLETE	0x0080
+
+/*
+ * The mechanism of our pfault code: if Linux is running as guest, runs a user
+ * space process and the user space process accesses a page that the host has
+ * paged out we get a pfault interrupt.
+ *
+ * This allows us, within the guest, to schedule a different process. Without
+ * this mechanism the host would have to suspend the whole virtual cpu until
+ * the page has been paged in.
+ *
+ * So when we get such an interrupt then we set the state of the current task
+ * to uninterruptible and also set the need_resched flag. Both happens within
+ * interrupt context(!). If we later on want to return to user space we
+ * recognize the need_resched flag and then call schedule().  It's not very
+ * obvious how this works...
+ *
+ * Of course we have a lot of additional fun with the completion interrupt (->
+ * host signals that a page of a process has been paged in and the process can
+ * continue to run). This interrupt can arrive on any cpu and, since we have
+ * virtual cpus, actually appear before the interrupt that signals that a page
+ * is missing.
+ */
+static void pfault_interrupt(struct ext_code ext_code,
+			     unsigned int param32, unsigned long param64)
+{
+	struct task_struct *tsk;
+	__u16 subcode;
+	pid_t pid;
+
+	/*
+	 * Get the external interruption subcode & pfault initial/completion
+	 * signal bit. VM stores this in the 'cpu address' field associated
+	 * with the external interrupt.
+	 */
+	subcode = ext_code.subcode;
+	if ((subcode & 0xff00) != __SUBCODE_MASK)
+		return;
+	inc_irq_stat(IRQEXT_PFL);
+	/* Get the token (= pid of the affected task). */
+	pid = param64 & LPP_PID_MASK;
+	rcu_read_lock();
+	tsk = find_task_by_pid_ns(pid, &init_pid_ns);
+	if (tsk)
+		get_task_struct(tsk);
+	rcu_read_unlock();
+	if (!tsk)
+		return;
+	spin_lock(&pfault_lock);
+	if (subcode & PF_COMPLETE) {
+		/* signal bit is set -> a page has been swapped in by VM */
+		if (tsk->thread.pfault_wait == 1) {
+			/* Initial interrupt was faster than the completion
+			 * interrupt. pfault_wait is valid. Set pfault_wait
+			 * back to zero and wake up the process. This can
+			 * safely be done because the task is still sleeping
+			 * and can't produce new pfaults. */
+			tsk->thread.pfault_wait = 0;
+			list_del(&tsk->thread.list);
+			wake_up_process(tsk);
+			put_task_struct(tsk);
+		} else {
+			/* Completion interrupt was faster than initial
+			 * interrupt. Set pfault_wait to -1 so the initial
+			 * interrupt doesn't put the task to sleep.
+			 * If the task is not running, ignore the completion
+			 * interrupt since it must be a leftover of a PFAULT
+			 * CANCEL operation which didn't remove all pending
+			 * completion interrupts. */
+			if (tsk->state == TASK_RUNNING)
+				tsk->thread.pfault_wait = -1;
+		}
+	} else {
+		/* signal bit not set -> a real page is missing. */
+		if (WARN_ON_ONCE(tsk != current))
+			goto out;
+		if (tsk->thread.pfault_wait == 1) {
+			/* Already on the list with a reference: put to sleep */
+			goto block;
+		} else if (tsk->thread.pfault_wait == -1) {
+			/* Completion interrupt was faster than the initial
+			 * interrupt (pfault_wait == -1). Set pfault_wait
+			 * back to zero and exit. */
+			tsk->thread.pfault_wait = 0;
+		} else {
+			/* Initial interrupt arrived before completion
+			 * interrupt. Let the task sleep.
+			 * An extra task reference is needed since a different
+			 * cpu may set the task state to TASK_RUNNING again
+			 * before the scheduler is reached. */
+			get_task_struct(tsk);
+			tsk->thread.pfault_wait = 1;
+			list_add(&tsk->thread.list, &pfault_list);
+block:
+			/* Since this must be a userspace fault, there
+			 * is no kernel task state to trample. Rely on the
+			 * return to userspace schedule() to block. */
+			__set_current_state(TASK_UNINTERRUPTIBLE);
+			set_tsk_need_resched(tsk);
+			set_preempt_need_resched();
+		}
+	}
+out:
+	spin_unlock(&pfault_lock);
+	put_task_struct(tsk);
+}
+
+static int pfault_cpu_dead(unsigned int cpu)
+{
+	struct thread_struct *thread, *next;
+	struct task_struct *tsk;
+
+	spin_lock_irq(&pfault_lock);
+	list_for_each_entry_safe(thread, next, &pfault_list, list) {
+		thread->pfault_wait = 0;
+		list_del(&thread->list);
+		tsk = container_of(thread, struct task_struct, thread);
+		wake_up_process(tsk);
+		put_task_struct(tsk);
+	}
+	spin_unlock_irq(&pfault_lock);
+	return 0;
+}
+
+static int __init pfault_irq_init(void)
+{
+	int rc;
+
+	rc = register_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
+	if (rc)
+		goto out_extint;
+	rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP;
+	if (rc)
+		goto out_pfault;
+	irq_subclass_register(IRQ_SUBCLASS_SERVICE_SIGNAL);
+	cpuhp_setup_state_nocalls(CPUHP_S390_PFAULT_DEAD, "s390/pfault:dead",
+				  NULL, pfault_cpu_dead);
+	return 0;
+
+out_pfault:
+	unregister_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
+out_extint:
+	pfault_disable = 1;
+	return rc;
+}
+early_initcall(pfault_irq_init);
+
+#endif /* CONFIG_PFAULT */