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[v2,1/2] x86/cpufeatures: Define X86_FEATURE_AMD_IBPB_RET

Message ID 20240816182533.2478415-1-jmattson@google.com (mailing list archive)
State New, archived
Headers show
Series [v2,1/2] x86/cpufeatures: Define X86_FEATURE_AMD_IBPB_RET | expand

Commit Message

Jim Mattson Aug. 16, 2024, 6:25 p.m. UTC 
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@chromium.org>
Signed-off-by: Jim Mattson <jmattson@google.com>
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 1 file changed, 1 insertion(+)
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Patch

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index dd4682857c12..e5bcb428dcf9 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -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 */