[PATCH v3 3/6] KVM: SEV: Disallow setting SNP-only features for non-SNP guests via a single mask

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

As SNP-only features get added, adding them to the valid_vmsa_features mask
in __sev_guest_init() often gets neglected.  Add SVM_SEV_FEAT_SNP_ONLY_MASK
to help group these common features together.

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 | 2 ++
 arch/x86/kvm/svm/sev.c     | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index edde36097ddc..7e3f9d92351a 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -307,6 +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 VMCB_ALLOWED_SEV_FEATURES_VALID			BIT_ULL(63)
 
 struct vmcb_seg {
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 3f9c1aa39a0a..2b4f3c05e282 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -456,7 +456,7 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp,
 		return -EINVAL;
 
 	if (!snp_active)
-		valid_vmsa_features &= ~SVM_SEV_FEAT_SECURE_TSC;
+		valid_vmsa_features &= ~SVM_SEV_FEAT_SNP_ONLY_MASK;
 
 	if (data->vmsa_features & ~valid_vmsa_features)
 		return -EINVAL;
-- 
2.43.0