linux-kernel - [PATCH v2 1/2] KVM: x86: Advertise EferLmsleUnsupported to userspace

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Message-ID: <20251001001529.1119031-2-jmattson@google.com>
Date: Tue, 30 Sep 2025 17:14:07 -0700
From: Jim Mattson <jmattson@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Tom Lendacky <thomas.lendacky@....com>, 
	Jim Mattson <jmattson@...gle.com>, Perry Yuan <perry.yuan@....com>, 
	Sohil Mehta <sohil.mehta@...el.com>, "Xin Li (Intel)" <xin@...or.com>, 
	Joerg Roedel <joerg.roedel@....com>, Avi Kivity <avi@...hat.com>, linux-kernel@...r.kernel.org, 
	kvm@...r.kernel.org, Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: [PATCH v2 1/2] KVM: x86: Advertise EferLmsleUnsupported to userspace

CPUID.80000008H:EBX.EferLmsleUnsupported[bit 20] is a defeature
bit. When this bit is clear, EFER.LMSLE is supported. When this bit is
set, EFER.LMLSE is unsupported. KVM has never supported EFER.LMSLE, so
it cannot support a 0-setting of this bit.

Pass through the bit in KVM_GET_SUPPORTED_CPUID to advertise the
unavailability of EFER.LMSLE to userspace.

Signed-off-by: Jim Mattson <jmattson@...gle.com>
---
 v1 -> v2:
   Pass through the bit from hardware, rather than forcing it to be set.

 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kvm/cpuid.c               | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 751ca35386b0..f9b593721917 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -338,6 +338,7 @@
 #define X86_FEATURE_AMD_STIBP		(13*32+15) /* Single Thread Indirect Branch Predictors */
 #define X86_FEATURE_AMD_STIBP_ALWAYS_ON	(13*32+17) /* Single Thread Indirect Branch Predictors always-on preferred */
 #define X86_FEATURE_AMD_IBRS_SAME_MODE	(13*32+19) /* Indirect Branch Restricted Speculation same mode protection*/
+#define X86_FEATURE_EFER_LMSLE_MBZ	(13*32+20) /* EFER.LMSLE must be zero */
 #define X86_FEATURE_AMD_PPIN		(13*32+23) /* "amd_ppin" Protected Processor Inventory Number */
 #define X86_FEATURE_AMD_SSBD		(13*32+24) /* Speculative Store Bypass Disable */
 #define X86_FEATURE_VIRT_SSBD		(13*32+25) /* "virt_ssbd" Virtualized Speculative Store Bypass Disable */
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index e2836a255b16..4823970611fd 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1096,6 +1096,7 @@ void kvm_set_cpu_caps(void)
 		F(AMD_STIBP),
 		F(AMD_STIBP_ALWAYS_ON),
 		F(AMD_IBRS_SAME_MODE),
+		F(EFER_LMSLE_MBZ),
 		F(AMD_PSFD),
 		F(AMD_IBPB_RET),
 	);
-- 
2.51.0.618.g983fd99d29-goog