[PATCH v3 4/6] KVM: SEV: Advertise SVM_SEV_FEAT_SNP_ACTIVE

[Kim Phillips <kim.phillips@amd.com>]

Allow userspace to set the flag in kvm_sev_init.flags.

KVM still needs to set the flag for backwards compatibility, but
disallowing SVM_SEV_FEAT_SNP_ACTIVE for an SNP guest is "bizarre."

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/kvm/aaWog_UjW-M3412C@google.com/
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
---
v3: new

 arch/x86/include/asm/svm.h | 3 ++-
 arch/x86/kvm/svm/sev.c     | 8 ++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 7e3f9d92351a..4f844a72890c 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -307,7 +307,8 @@ static_assert((X2AVIC_4K_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == X2AV
 #define SVM_SEV_FEAT_DEBUG_SWAP				BIT(5)
 #define SVM_SEV_FEAT_SECURE_TSC				BIT(9)
 
-#define SVM_SEV_FEAT_SNP_ONLY_MASK	SVM_SEV_FEAT_SECURE_TSC
+#define SVM_SEV_FEAT_SNP_ONLY_MASK	(SVM_SEV_FEAT_SNP_ACTIVE | \
+					 SVM_SEV_FEAT_SECURE_TSC)
 
 #define VMCB_ALLOWED_SEV_FEATURES_VALID			BIT_ULL(63)
 
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 2b4f3c05e282..9663424c0cf0 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3165,8 +3165,12 @@ void __init sev_hardware_setup(void)
 	    cpu_feature_enabled(X86_FEATURE_NO_NESTED_DATA_BP))
 		sev_supported_vmsa_features |= SVM_SEV_FEAT_DEBUG_SWAP;
 
-	if (sev_snp_enabled && tsc_khz && cpu_feature_enabled(X86_FEATURE_SNP_SECURE_TSC))
-		sev_supported_vmsa_features |= SVM_SEV_FEAT_SECURE_TSC;
+	if (sev_snp_enabled) {
+		sev_supported_vmsa_features |= SVM_SEV_FEAT_SNP_ACTIVE;
+
+		if (tsc_khz && cpu_feature_enabled(X86_FEATURE_SNP_SECURE_TSC))
+			sev_supported_vmsa_features |= SVM_SEV_FEAT_SECURE_TSC;
+	}
 }
 
 void sev_hardware_unsetup(void)
-- 
2.43.0