arch/x86/include/asm/switch_to.h

   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 *prev,
  17                                      struct task_struct *next)
  18 {
  19 #ifdef CONFIG_VMAP_STACK
  20         /*
  21          * If we switch to a stack that has a top-level paging entry
  22          * that is not present in the current mm, the resulting #PF will
  23          * will be promoted to a double-fault and we'll panic.  Probe
  24          * the new stack now so that vmalloc_fault can fix up the page
  25          * tables if needed.  This can only happen if we use a stack
  26          * in vmap space.
  27          *
  28          * We assume that the stack is aligned so that it never spans
  29          * more than one top-level paging entry.
  30          *
  31          * To minimize cache pollution, just follow the stack pointer.
  32          */
  33         READ_ONCE(*(unsigned char *)next->thread.sp);
  34 #endif
  35 }
  36
  37 asmlinkage void ret_from_fork(void);
  38
  39 /*
  40  * This is the structure pointed to by thread.sp for an inactive task.  The
  41  * order of the fields must match the code in __switch_to_asm().
  42  */
  43 struct inactive_task_frame {
  44         unsigned long flags;
  45 #ifdef CONFIG_X86_64
  46         unsigned long r15;
  47         unsigned long r14;
  48         unsigned long r13;
  49         unsigned long r12;
  50 #else
  51         unsigned long si;
  52         unsigned long di;
  53 #endif
  54         unsigned long bx;
  55
  56         /*
  57          * These two fields must be together.  They form a stack frame header,
  58          * needed by get_frame_pointer().
  59          */
  60         unsigned long bp;
  61         unsigned long ret_addr;
  62 };
  63
  64 struct fork_frame {
  65         struct inactive_task_frame frame;
  66         struct pt_regs regs;
  67 };
  68
  69 #define switch_to(prev, next, last)                                     \
  70 do {                                                                    \
  71         prepare_switch_to(prev, next);                                  \
  72                                                                         \
  73         ((last) = __switch_to_asm((prev), (next)));                     \
  74 } while (0)
  75
  76 #ifdef CONFIG_X86_32
  77 static inline void refresh_sysenter_cs(struct thread_struct *thread)
  78 {
  79         /* Only happens when SEP is enabled, no need to test "SEP"arately: */
  80         if (unlikely(this_cpu_read(cpu_tss_rw.x86_tss.ss1) == thread->sysenter_cs))
  81                 return;
  82
  83         this_cpu_write(cpu_tss_rw.x86_tss.ss1, thread->sysenter_cs);
  84         wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0);
  85 }
  86 #endif
  87
  88 /* This is used when switching tasks or entering/exiting vm86 mode. */
  89 static inline void update_sp0(struct task_struct *task)
  90 {
  91         /* On x86_64, sp0 always points to the entry trampoline stack, which is constant: */
  92 #ifdef CONFIG_X86_32
  93         load_sp0(task->thread.sp0);
  94 #else
  95         if (static_cpu_has(X86_FEATURE_XENPV))
  96                 load_sp0(task_top_of_stack(task));
  97 #endif
  98 }
  99
 100 #endif /* _ASM_X86_SWITCH_TO_H */