1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _ASM_X86_SWITCH_TO_H
3 #define _ASM_X86_SWITCH_TO_H
5 #include <linux/sched/task_stack.h>
7 struct task_struct; /* one of the stranger aspects of C forward declarations */
9 struct task_struct *__switch_to_asm(struct task_struct *prev,
10 struct task_struct *next);
12 __visible struct task_struct *__switch_to(struct task_struct *prev,
13 struct task_struct *next);
15 /* This runs runs on the previous thread's stack. */
16 static inline void prepare_switch_to(struct task_struct *next)
18 #ifdef CONFIG_VMAP_STACK
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
27 * We assume that the stack is aligned so that it never spans
28 * more than one top-level paging entry.
30 * To minimize cache pollution, just follow the stack pointer.
32 READ_ONCE(*(unsigned char *)next->thread.sp);
36 asmlinkage void ret_from_fork(void);
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().
42 struct inactive_task_frame {
56 * These two fields must be together. They form a stack frame header,
57 * needed by get_frame_pointer().
60 unsigned long ret_addr;
64 struct inactive_task_frame frame;
68 #define switch_to(prev, next, last) \
70 prepare_switch_to(next); \
72 ((last) = __switch_to_asm((prev), (next))); \
76 static inline void refresh_sysenter_cs(struct thread_struct *thread)
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))
82 this_cpu_write(cpu_tss_rw.x86_tss.ss1, thread->sysenter_cs);
83 wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0);
87 /* This is used when switching tasks or entering/exiting vm86 mode. */
88 static inline void update_task_stack(struct task_struct *task)
90 /* sp0 always points to the entry trampoline stack, which is constant: */
92 if (static_cpu_has(X86_FEATURE_XENPV))
93 load_sp0(task->thread.sp0);
95 this_cpu_write(cpu_tss_rw.x86_tss.sp1, task->thread.sp0);
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).
103 if (static_cpu_has(X86_FEATURE_XENPV))
104 load_sp0(task_top_of_stack(task));
108 static inline void kthread_frame_init(struct inactive_task_frame *frame,
109 unsigned long fun, unsigned long arg)
119 #endif /* _ASM_X86_SWITCH_TO_H */