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 *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 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
  62 struct fork_frame {
  63         struct inactive_task_frame frame;
  64         struct pt_regs regs;
  65 };
  66
  67 #define switch_to(prev, next, last)                                     \
  68 do {                                                                    \
  69         prepare_switch_to(next);                                        \
  70                                                                         \
  71         ((last) = __switch_to_asm((prev), (next)));                     \
  72 } while (0)
  73
  74 #ifdef CONFIG_X86_32
  75 static 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. */
  87 static 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 */