1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _ASM_X86_SWITCH_TO_H
3#define _ASM_X86_SWITCH_TO_H
4
5#include <linux/sched/task_stack.h>
6
7struct task_struct; /* one of the stranger aspects of C forward declarations */
8
9struct task_struct *__switch_to_asm(struct task_struct *prev,
10 struct task_struct *next);
11
12__visible struct task_struct *__switch_to(struct task_struct *prev,
13 struct task_struct *next);
14
15/* This runs runs on the previous thread's stack. */
16static inline void prepare_switch_to(struct task_struct *next)
17{
18#ifdef CONFIG_VMAP_STACK
19 /*
20 * If we switch to a stack that has a top-level paging entry
21 * that is not present in the current mm, the resulting #PF will
22 * will be promoted to a double-fault and we'll panic. Probe
23 * the new stack now so that vmalloc_fault can fix up the page
24 * tables if needed. This can only happen if we use a stack
25 * in vmap space.
26 *
27 * We assume that the stack is aligned so that it never spans
28 * more than one top-level paging entry.
29 *
30 * To minimize cache pollution, just follow the stack pointer.
31 */
32 READ_ONCE(*(unsigned char *)next->thread.sp);
33#endif
34}
35
36asmlinkage void ret_from_fork(void);
37
38/*
39 * This is the structure pointed to by thread.sp for an inactive task. The
40 * order of the fields must match the code in __switch_to_asm().
41 */
42struct inactive_task_frame {
43#ifdef CONFIG_X86_64
44 unsigned long r15;
45 unsigned long r14;
46 unsigned long r13;
47 unsigned long r12;
48#else
49 unsigned long si;
50 unsigned long di;
51#endif
52 unsigned long bx;
53
54 /*
55 * These two fields must be together. They form a stack frame header,
56 * needed by get_frame_pointer().
57 */
58 unsigned long bp;
59 unsigned long ret_addr;
60};
61
62struct fork_frame {
63 struct inactive_task_frame frame;
64 struct pt_regs regs;
65};
66
67#define switch_to(prev, next, last) \
68do { \
69 prepare_switch_to(next); \
70 \
71 ((last) = __switch_to_asm((prev), (next))); \
72} while (0)
73
74#ifdef CONFIG_X86_32
75static inline void refresh_sysenter_cs(struct thread_struct *thread)
76{
77 /* Only happens when SEP is enabled, no need to test "SEP"arately: */
78 if (unlikely(this_cpu_read(cpu_tss_rw.x86_tss.ss1) == thread->sysenter_cs))
79 return;
80
81 this_cpu_write(cpu_tss_rw.x86_tss.ss1, thread->sysenter_cs);
82 wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0);
83}
84#endif
85
86/* This is used when switching tasks or entering/exiting vm86 mode. */
87static inline void update_task_stack(struct task_struct *task)
88{
89 /* sp0 always points to the entry trampoline stack, which is constant: */
90#ifdef CONFIG_X86_32
91 if (static_cpu_has(X86_FEATURE_XENPV))
92 load_sp0(task->thread.sp0);
93 else
94 this_cpu_write(cpu_tss_rw.x86_tss.sp1, task->thread.sp0);
95#else
96 /*
97 * x86-64 updates x86_tss.sp1 via cpu_current_top_of_stack. That
98 * doesn't work on x86-32 because sp1 and
99 * cpu_current_top_of_stack have different values (because of
100 * the non-zero stack-padding on 32bit).
101 */
102 if (static_cpu_has(X86_FEATURE_XENPV))
103 load_sp0(task_top_of_stack(task));
104#endif
105
106}
107
108#endif /* _ASM_X86_SWITCH_TO_H */
109