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
7 struct task_struct; /* one of the stranger aspects of C forward declarations */
8
9 struct 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. */
16 static 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
36 asmlinkage 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 */
42 struct 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 flags;
50 unsigned long si;
51 unsigned long di;
52 #endif
53 unsigned long bx;
54
55 /*
56 * These two fields must be together. They form a stack frame header,
57 * needed by get_frame_pointer().
58 */
59 unsigned long bp;
60 unsigned long ret_addr;
61 };
62
63 struct fork_frame {
64 struct inactive_task_frame frame;
65 struct pt_regs regs;
66 };
67
68 #define switch_to(prev, next, last) \
69 do { \
70 prepare_switch_to(next); \
71 \
72 ((last) = __switch_to_asm((prev), (next))); \
73 } while (0)
74
75 #ifdef CONFIG_X86_32
76 static inline void refresh_sysenter_cs(struct thread_struct *thread)
77 {
78 /* Only happens when SEP is enabled, no need to test "SEP"arately: */
79 if (unlikely(this_cpu_read(cpu_tss_rw.x86_tss.ss1) == thread->sysenter_cs))
80 return;
81
82 this_cpu_write(cpu_tss_rw.x86_tss.ss1, thread->sysenter_cs);
83 wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0);
84 }
85 #endif
86
87 /* This is used when switching tasks or entering/exiting vm86 mode. */
88 static inline void update_task_stack(struct task_struct *task)
89 {
90 /* sp0 always points to the entry trampoline stack, which is constant: */
91 #ifdef CONFIG_X86_32
92 if (static_cpu_has(X86_FEATURE_XENPV))
93 load_sp0(task->thread.sp0);
94 else
95 this_cpu_write(cpu_tss_rw.x86_tss.sp1, task->thread.sp0);
96 #else
97 /*
98 * x86-64 updates x86_tss.sp1 via cpu_current_top_of_stack. That
99 * doesn't work on x86-32 because sp1 and
100 * cpu_current_top_of_stack have different values (because of
101 * the non-zero stack-padding on 32bit).
102 */
103 if (static_cpu_has(X86_FEATURE_XENPV))
104 load_sp0(task_top_of_stack(task));
105 #endif
106
107 }
108
109 #endif /* _ASM_X86_SWITCH_TO_H */