arch/x86/kernel/process.h

   1 // SPDX-License-Identifier: GPL-2.0
   2 //
   3 // Code shared between 32 and 64 bit
   4
   5 #include <asm/spec-ctrl.h>
   6
   7 void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p);
   8
   9 /*
  10  * This needs to be inline to optimize for the common case where no extra
  11  * work needs to be done.
  12  */
  13 static inline void switch_to_extra(struct task_struct *prev,
  14                                    struct task_struct *next)
  15 {
  16         unsigned long next_tif = task_thread_info(next)->flags;
  17         unsigned long prev_tif = task_thread_info(prev)->flags;
  18
  19         if (IS_ENABLED(CONFIG_SMP)) {
  20                 /*
  21                  * Avoid __switch_to_xtra() invocation when conditional
  22                  * STIBP is disabled and the only different bit is
  23                  * TIF_SPEC_IB. For CONFIG_SMP=n TIF_SPEC_IB is not
  24                  * in the TIF_WORK_CTXSW masks.
  25                  */
  26                 if (!static_branch_likely(&switch_to_cond_stibp)) {
  27                         prev_tif &= ~_TIF_SPEC_IB;
  28                         next_tif &= ~_TIF_SPEC_IB;
  29                 }
  30         }
  31
  32         /*
  33          * __switch_to_xtra() handles debug registers, i/o bitmaps,
  34          * speculation mitigations etc.
  35          */
  36         if (unlikely(next_tif & _TIF_WORK_CTXSW_NEXT ||
  37                      prev_tif & _TIF_WORK_CTXSW_PREV))
  38                 __switch_to_xtra(prev, next);
  39 }