[PATCH v4 1/3] x86/cpufeatures: Define X86_FEATURE_AMD_IBPB_RET

[Jim Mattson]

AMD's initial implementation of IBPB did not clear the return address
predictor. Beginning with Zen4, AMD's IBPB *does* clear the return
address predictor. This behavior is enumerated by
CPUID.80000008H:EBX.IBPB_RET[bit 30].

Define X86_FEATURE_AMD_IBPB_RET for use in KVM_GET_SUPPORTED_CPUID,
when determining cross-vendor capabilities.

Suggested-by: Venkatesh Srinivas <venkateshs@xxxxxxxxxxxx>
Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
---
 arch/x86/include/asm/cpufeatures.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index cabd6b58e8ec..a222a24677d7 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -215,7 +215,7 @@
 #define X86_FEATURE_SPEC_STORE_BYPASS_DISABLE	( 7*32+23) /* Disable Speculative Store Bypass. */
 #define X86_FEATURE_LS_CFG_SSBD		( 7*32+24)  /* AMD SSBD implementation via LS_CFG MSR */
 #define X86_FEATURE_IBRS		( 7*32+25) /* "ibrs" Indirect Branch Restricted Speculation */
-#define X86_FEATURE_IBPB		( 7*32+26) /* "ibpb" Indirect Branch Prediction Barrier without RSB flush */
+#define X86_FEATURE_IBPB		( 7*32+26) /* "ibpb" Indirect Branch Prediction Barrier without a guaranteed RSB flush */
 #define X86_FEATURE_STIBP		( 7*32+27) /* "stibp" Single Thread Indirect Branch Predictors */
 #define X86_FEATURE_ZEN			( 7*32+28) /* Generic flag for all Zen and newer */
 #define X86_FEATURE_L1TF_PTEINV		( 7*32+29) /* L1TF workaround PTE inversion */
@@ -348,6 +348,7 @@
 #define X86_FEATURE_CPPC		(13*32+27) /* "cppc" Collaborative Processor Performance Control */
 #define X86_FEATURE_AMD_PSFD            (13*32+28) /* Predictive Store Forwarding Disable */
 #define X86_FEATURE_BTC_NO		(13*32+29) /* Not vulnerable to Branch Type Confusion */
+#define X86_FEATURE_AMD_IBPB_RET	(13*32+30) /* IBPB clears return address predictor */
 #define X86_FEATURE_BRS			(13*32+31) /* "brs" Branch Sampling available */
 
 /* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */
-- 
2.46.0.662.g92d0881bb0-goog