16413 Post-barrier Return Stack Buffer (consider no-eIBRS cases)
16413 Post-barrier Return Stack Buffer (PBRSB) fixes can be detected in HW

*** 932,941 ****
--- 932,942 ----
  #define X86FSET_AVX512_VBMI2    106
  #define X86FSET_AVX512_BF16     107
  #define X86FSET_AUTO_IBRS       108
  #define X86FSET_RFDS_NO         109
  #define X86FSET_RFDS_CLEAR      110
+ #define X86FSET_PBRSB_NO        111
  
  /*
   * Intel Deep C-State invariant TSC in leaf 0x80000007.
   */
  #define CPUID_TSC_CSTATE_INVARIANCE     (0x100)
*** 1584,1594 ****
  
  #if !defined(_ASM)
  
  #if defined(_KERNEL) || defined(_KMEMUSER)
  
! #define NUM_X86_FEATURES        111
  extern uchar_t x86_featureset[];
  
  extern void free_x86_featureset(void *featureset);
  extern boolean_t is_x86_feature(void *featureset, uint_t feature);
  extern void add_x86_feature(void *featureset, uint_t feature);
--- 1585,1595 ----
  
  #if !defined(_ASM)
  
  #if defined(_KERNEL) || defined(_KMEMUSER)
  
! #define NUM_X86_FEATURES        112
  extern uchar_t x86_featureset[];
  
  extern void free_x86_featureset(void *featureset);
  extern boolean_t is_x86_feature(void *featureset, uint_t feature);
  extern void add_x86_feature(void *featureset, uint_t feature);
*** 1607,1616 ****
--- 1608,1618 ----
   * These functions are all used to perform various side-channel mitigations.
   * Please see uts/i86pc/os/cpuid.c for more information.
   */
  extern void (*spec_uarch_flush)(void);
  extern void x86_rsb_stuff(void);
+ extern void x86_rsb_stuff_vmexit(void);
  extern void x86_md_clear(void);
  
  #endif
  
  #if defined(_KERNEL)