On 7/16/25 00:56, Nikunj A Dadhania wrote:

Require a minimum GHCB version of 2 when starting SEV-SNP guests through KVM_SEV_INIT2. When a VMM attempts to start an SEV-SNP guest with an incompatible GHCB version (less than 2), reject the request early rather than allowing the guest kernel to start with an incorrect protocol version and fail later with GHCB_SNP_UNSUPPORTED guest termination.

Hypervisor logs the guest termination with GHCB_SNP_UNSUPPORTED error code:

kvm_amd: SEV-ES guest requested termination: 0x0:0x2

SNP guest fails with the below error message:

KVM: unknown exit reason 24 EAX=00000000 EBX=00000000 ECX=00000000 EDX=00a00f11 ESI=00000000 EDI=00000000 EBP=00000000 ESP=00000000 EIP=0000fff0 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0 ES =0000 00000000 0000ffff 00009300 CS =f000 ffff0000 0000ffff 00009b00 SS =0000 00000000 0000ffff 00009300 DS =0000 00000000 0000ffff 00009300 FS =0000 00000000 0000ffff 00009300 GS =0000 00000000 0000ffff 00009300 LDT=0000 00000000 0000ffff 00008200 TR =0000 00000000 0000ffff 00008b00 GDT= 00000000 0000ffff IDT= 00000000 0000ffff CR0=60000010 CR2=00000000 CR3=00000000 CR4=00000000 DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 DR6=00000000ffff0ff0 DR7=0000000000000400 EFER=0000000000000000

Fixes: 4af663c2f64a ("KVM: SEV: Allow per-guest configuration of GHCB protocol version") Cc: Thomas Lendacky thomas.lendacky@amd.com Cc: Sean Christopherson seanjc@google.com Cc: Michael Roth michael.roth@amd.com Cc: stable@vger.kernel.org

You kept the stable email.

Minor comment below about placement, but otherwise...

Reviewed-by: Tom Lendacky thomas.lendacky@amd.com

Signed-off-by: Nikunj A Dadhania nikunj@amd.com

---

Changes since v1:

• Add failure logs in the commit and drop @stable tag (Sean)

---

arch/x86/kvm/svm/sev.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 95668e84ab86..fdc1309c68cb 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -406,6 +406,7 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp, struct kvm_sev_info *sev = to_kvm_sev_info(kvm); struct sev_platform_init_args init_args = {0}; bool es_active = vm_type != KVM_X86_SEV_VM;

• bool snp_active = vm_type == KVM_X86_SNP_VM; u64 valid_vmsa_features = es_active ? sev_supported_vmsa_features : 0; int ret;

@@ -424,6 +425,9 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp, if (unlikely(sev->active)) return -EINVAL;

• if (snp_active && data->ghcb_version && data->ghcb_version < 2)

• return -EINVAL;
  

Would it make sense to move this up a little bit so that it follows the other ghcb_version check? This way the checks are grouped.

Thanks, Tom

sev->active = true; sev->es_active = es_active; sev->vmsa_features = data->vmsa_features; @@ -437,7 +441,7 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp, if (sev->es_active && !sev->ghcb_version) sev->ghcb_version = GHCB_VERSION_DEFAULT;

• if (vm_type == KVM_X86_SNP_VM)

• if (snp_active) sev->vmsa_features |= SVM_SEV_FEAT_SNP_ACTIVE;

ret = sev_asid_new(sev); @@ -455,7 +459,7 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp, } /* This needs to happen after SEV/SNP firmware initialization. */

• if (vm_type == KVM_X86_SNP_VM) {

• if (snp_active) { ret = snp_guest_req_init(kvm); if (ret) goto e_free;

base-commit: 772d50d9b87bec08b56ecee0a880d6b2ee5c7da5