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

@@ -932,10 +932,11 @@
 #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)

@@ -1584,11 +1585,11 @@
 
 #if !defined(_ASM)
 
 #if defined(_KERNEL) || defined(_KMEMUSER)
 
-#define NUM_X86_FEATURES        111
+#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);

@@ -1607,10 +1608,11 @@
  * 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)