1 files changed, 109 insertions, 0 deletions
diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
new file mode 100644
index 000000000..157149d41
--- /dev/null
+++ b/arch/x86/include/asm/switch_to.h
@@ -0,0 +1,109 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_SWITCH_TO_H
+#define _ASM_X86_SWITCH_TO_H
+
+#include <linux/sched/task_stack.h>
+
+struct task_struct; /* one of the stranger aspects of C forward declarations */
+
+struct task_struct *__switch_to_asm(struct task_struct *prev,
+				    struct task_struct *next);
+
+__visible struct task_struct *__switch_to(struct task_struct *prev,
+					  struct task_struct *next);
+
+/* This runs runs on the previous thread's stack. */
+static inline void prepare_switch_to(struct task_struct *next)
+{
+#ifdef CONFIG_VMAP_STACK
+	/*
+	 * If we switch to a stack that has a top-level paging entry
+	 * that is not present in the current mm, the resulting #PF will
+	 * will be promoted to a double-fault and we'll panic.  Probe
+	 * the new stack now so that vmalloc_fault can fix up the page
+	 * tables if needed.  This can only happen if we use a stack
+	 * in vmap space.
+	 *
+	 * We assume that the stack is aligned so that it never spans
+	 * more than one top-level paging entry.
+	 *
+	 * To minimize cache pollution, just follow the stack pointer.
+	 */
+	READ_ONCE(*(unsigned char *)next->thread.sp);
+#endif
+}
+
+asmlinkage void ret_from_fork(void);
+
+/*
+ * This is the structure pointed to by thread.sp for an inactive task.  The
+ * order of the fields must match the code in __switch_to_asm().
+ */
+struct inactive_task_frame {
+	unsigned long flags;
+#ifdef CONFIG_X86_64
+	unsigned long r15;
+	unsigned long r14;
+	unsigned long r13;
+	unsigned long r12;
+#else
+	unsigned long si;
+	unsigned long di;
+#endif
+	unsigned long bx;
+
+	/*
+	 * These two fields must be together.  They form a stack frame header,
+	 * needed by get_frame_pointer().
+	 */
+	unsigned long bp;
+	unsigned long ret_addr;
+};
+
+struct fork_frame {
+	struct inactive_task_frame frame;
+	struct pt_regs regs;
+};
+
+#define switch_to(prev, next, last)					\
+do {									\
+	prepare_switch_to(next);					\
+									\
+	((last) = __switch_to_asm((prev), (next)));			\
+} while (0)
+
+#ifdef CONFIG_X86_32
+static inline void refresh_sysenter_cs(struct thread_struct *thread)
+{
+	/* Only happens when SEP is enabled, no need to test "SEP"arately: */
+	if (unlikely(this_cpu_read(cpu_tss_rw.x86_tss.ss1) == thread->sysenter_cs))
+		return;
+
+	this_cpu_write(cpu_tss_rw.x86_tss.ss1, thread->sysenter_cs);
+	wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0);
+}
+#endif
+
+/* This is used when switching tasks or entering/exiting vm86 mode. */
+static inline void update_task_stack(struct task_struct *task)
+{
+	/* sp0 always points to the entry trampoline stack, which is constant: */
+#ifdef CONFIG_X86_32
+	if (static_cpu_has(X86_FEATURE_XENPV))
+		load_sp0(task->thread.sp0);
+	else
+		this_cpu_write(cpu_tss_rw.x86_tss.sp1, task->thread.sp0);
+#else
+	/*
+	 * x86-64 updates x86_tss.sp1 via cpu_current_top_of_stack. That
+	 * doesn't work on x86-32 because sp1 and
+	 * cpu_current_top_of_stack have different values (because of
+	 * the non-zero stack-padding on 32bit).
+	 */
+	if (static_cpu_has(X86_FEATURE_XENPV))
+		load_sp0(task_top_of_stack(task));
+#endif
+
+}
+
+#endif /* _ASM_X86_SWITCH_TO_H */