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       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 flags;
      50                 :            :         unsigned long si;
      51                 :            :         unsigned long di;
      52                 :            : #endif
      53                 :            :         unsigned long bx;
      54                 :            : 
      55                 :            :         /*
      56                 :            :          * These two fields must be together.  They form a stack frame header,
      57                 :            :          * needed by get_frame_pointer().
      58                 :            :          */
      59                 :            :         unsigned long bp;
      60                 :            :         unsigned long ret_addr;
      61                 :            : };
      62                 :            : 
      63                 :            : struct fork_frame {
      64                 :            :         struct inactive_task_frame frame;
      65                 :            :         struct pt_regs regs;
      66                 :            : };
      67                 :            : 
      68                 :            : #define switch_to(prev, next, last)                                     \
      69                 :            : do {                                                                    \
      70                 :            :         prepare_switch_to(next);                                        \
      71                 :            :                                                                         \
      72                 :            :         ((last) = __switch_to_asm((prev), (next)));                     \
      73                 :            : } while (0)
      74                 :            : 
      75                 :            : #ifdef CONFIG_X86_32
      76                 :            : static inline void refresh_sysenter_cs(struct thread_struct *thread)
      77                 :            : {
      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))
      80                 :            :                 return;
      81                 :            : 
      82                 :            :         this_cpu_write(cpu_tss_rw.x86_tss.ss1, thread->sysenter_cs);
      83                 :            :         wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0);
      84                 :            : }
      85                 :            : #endif
      86                 :            : 
      87                 :            : /* This is used when switching tasks or entering/exiting vm86 mode. */
      88                 :      84205 : static inline void update_task_stack(struct task_struct *task)
      89                 :            : {
      90                 :            :         /* sp0 always points to the entry trampoline stack, which is constant: */
      91                 :            : #ifdef CONFIG_X86_32
      92                 :            :         if (static_cpu_has(X86_FEATURE_XENPV))
      93                 :            :                 load_sp0(task->thread.sp0);
      94                 :            :         else
      95                 :            :                 this_cpu_write(cpu_tss_rw.x86_tss.sp1, task->thread.sp0);
      96                 :            : #else
      97                 :            :         /*
      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).
     102                 :            :          */
     103      [ -  -  + ]:      84205 :         if (static_cpu_has(X86_FEATURE_XENPV))
     104                 :          0 :                 load_sp0(task_top_of_stack(task));
     105                 :            : #endif
     106                 :      84205 : }
     107                 :            : 
     108                 :        302 : static inline void kthread_frame_init(struct inactive_task_frame *frame,
     109                 :            :                                       unsigned long fun, unsigned long arg)
     110                 :            : {
     111                 :        302 :         frame->bx = fun;
     112                 :            : #ifdef CONFIG_X86_32
     113                 :            :         frame->di = arg;
     114                 :            : #else
     115                 :        302 :         frame->r12 = arg;
     116                 :            : #endif
     117                 :            : }
     118                 :            : 
     119                 :            : #endif /* _ASM_X86_SWITCH_TO_H */