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 struct tss_struct;
  15 void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
  16                       struct tss_struct *tss);
  17
  18 /* This runs runs on the previous thread's stack. */
  19 static inline void prepare_switch_to(struct task_struct *prev,
  20                                      struct task_struct *next)
  21 {
  22 #ifdef CONFIG_VMAP_STACK
  23         /*
  24          * If we switch to a stack that has a top-level paging entry
  25          * that is not present in the current mm, the resulting #PF will
  26          * will be promoted to a double-fault and we'll panic.  Probe
  27          * the new stack now so that vmalloc_fault can fix up the page
  28          * tables if needed.  This can only happen if we use a stack
  29          * in vmap space.
  30          *
  31          * We assume that the stack is aligned so that it never spans
  32          * more than one top-level paging entry.
  33          *
  34          * To minimize cache pollution, just follow the stack pointer.
  35          */
  36         READ_ONCE(*(unsigned char *)next->thread.sp);
  37 #endif
  38 }
  39
  40 asmlinkage void ret_from_fork(void);
  41
  42 /*
  43  * This is the structure pointed to by thread.sp for an inactive task.  The
  44  * order of the fields must match the code in __switch_to_asm().
  45  */
  46 struct inactive_task_frame {
  47 #ifdef CONFIG_X86_64
  48         unsigned long r15;
  49         unsigned long r14;
  50         unsigned long r13;
  51         unsigned long r12;
  52 #else
  53         unsigned long si;
  54         unsigned long di;
  55 #endif
  56         unsigned long bx;
  57
  58         /*
  59          * These two fields must be together.  They form a stack frame header,
  60          * needed by get_frame_pointer().
  61          */
  62         unsigned long bp;
  63         unsigned long ret_addr;
  64 };
  65
  66 struct fork_frame {
  67         struct inactive_task_frame frame;
  68         struct pt_regs regs;
  69 };
  70
  71 #define switch_to(prev, next, last)                                     \
  72 do {                                                                    \
  73         prepare_switch_to(prev, next);                                  \
  74                                                                         \
  75         ((last) = __switch_to_asm((prev), (next)));                     \
  76 } while (0)
  77
  78 #ifdef CONFIG_X86_32
  79 static inline void refresh_sysenter_cs(struct thread_struct *thread)
  80 {
  81         /* Only happens when SEP is enabled, no need to test "SEP"arately: */
  82         if (unlikely(this_cpu_read(cpu_tss_rw.x86_tss.ss1) == thread->sysenter_cs))
  83                 return;
  84
  85         this_cpu_write(cpu_tss_rw.x86_tss.ss1, thread->sysenter_cs);
  86         wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0);
  87 }
  88 #endif
  89
  90 /* This is used when switching tasks or entering/exiting vm86 mode. */
  91 static inline void update_sp0(struct task_struct *task)
  92 {
  93         /* On x86_64, sp0 always points to the entry trampoline stack, which is constant: */
  94 #ifdef CONFIG_X86_32
  95         load_sp0(task->thread.sp0);
  96 #else
  97         if (static_cpu_has(X86_FEATURE_XENPV))
  98                 load_sp0(task_top_of_stack(task));
  99 #endif
 100 }
 101
 102 #endif /* _ASM_X86_SWITCH_TO_H */