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 *next)
  20 {
  21 #ifdef CONFIG_VMAP_STACK
  22         /*
  23          * If we switch to a stack that has a top-level paging entry
  24          * that is not present in the current mm, the resulting #PF will
  25          * will be promoted to a double-fault and we'll panic.  Probe
  26          * the new stack now so that vmalloc_fault can fix up the page
  27          * tables if needed.  This can only happen if we use a stack
  28          * in vmap space.
  29          *
  30          * We assume that the stack is aligned so that it never spans
  31          * more than one top-level paging entry.
  32          *
  33          * To minimize cache pollution, just follow the stack pointer.
  34          */
  35         READ_ONCE(*(unsigned char *)next->thread.sp);
  36 #endif
  37 }
  38
  39 asmlinkage void ret_from_fork(void);
  40
  41 /*
  42  * This is the structure pointed to by thread.sp for an inactive task.  The
  43  * order of the fields must match the code in __switch_to_asm().
  44  */
  45 struct inactive_task_frame {
  46 #ifdef CONFIG_X86_64
  47         unsigned long r15;
  48         unsigned long r14;
  49         unsigned long r13;
  50         unsigned long r12;
  51 #else
  52         unsigned long si;
  53         unsigned long di;
  54 #endif
  55         unsigned long bx;
  56
  57         /*
  58          * These two fields must be together.  They form a stack frame header,
  59          * needed by get_frame_pointer().
  60          */
  61         unsigned long bp;
  62         unsigned long ret_addr;
  63 };
  64
  65 struct fork_frame {
  66         struct inactive_task_frame frame;
  67         struct pt_regs regs;
  68 };
  69
  70 #define switch_to(prev, next, last)                                     \
  71 do {                                                                    \
  72         prepare_switch_to(next);                                        \
  73                                                                         \
  74         ((last) = __switch_to_asm((prev), (next)));                     \
  75 } while (0)
  76
  77 #ifdef CONFIG_X86_32
  78 static inline void refresh_sysenter_cs(struct thread_struct *thread)
  79 {
  80         /* Only happens when SEP is enabled, no need to test "SEP"arately: */
  81         if (unlikely(this_cpu_read(cpu_tss_rw.x86_tss.ss1) == thread->sysenter_cs))
  82                 return;
  83
  84         this_cpu_write(cpu_tss_rw.x86_tss.ss1, thread->sysenter_cs);
  85         wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0);
  86 }
  87 #endif
  88
  89 /* This is used when switching tasks or entering/exiting vm86 mode. */
  90 static inline void update_task_stack(struct task_struct *task)
  91 {
  92         /* sp0 always points to the entry trampoline stack, which is constant: */
  93 #ifdef CONFIG_X86_32
  94         if (static_cpu_has(X86_FEATURE_XENPV))
  95                 load_sp0(task->thread.sp0);
  96         else
  97                 this_cpu_write(cpu_tss_rw.x86_tss.sp1, task->thread.sp0);
  98 #else
  99         /*
 100          * x86-64 updates x86_tss.sp1 via cpu_current_top_of_stack. That
 101          * doesn't work on x86-32 because sp1 and
 102          * cpu_current_top_of_stack have different values (because of
 103          * the non-zero stack-padding on 32bit).
 104          */
 105         if (static_cpu_has(X86_FEATURE_XENPV))
 106                 load_sp0(task_top_of_stack(task));
 107 #endif
 108
 109 }
 110
 111 #endif /* _ASM_X86_SWITCH_TO_H */