On 2/18/25 19:27, Sean Christopherson wrote:
> When handling an "AP Create" event, return an error if the "requested" SEV
> features for the vCPU don't exactly match KVM's view of the VM-scoped
> features. There is no known use case for heterogeneous SEV features across
> vCPUs, and while KVM can't actually enforce an exact match since the value
> in RAX isn't guaranteed to match what the guest shoved into the VMSA, KVM
> can at least avoid knowingly letting the guest run in an unsupported state.
>
> E.g. if a VM is created with DebugSwap disabled, KVM will intercept #DBs
> and DRs for all vCPUs, even if an AP is "created" with DebugSwap enabled in
> its VMSA.
>
> Note, the GHCB spec only "requires" that "AP use the same interrupt
> injection mechanism as the BSP", but given the disaster that is DebugSwap
> and SEV_FEATURES in general, it's safe to say that AMD didn't consider all
> possible complications with mismatching features between the BSP and APs.
>
> Oppurtunistically fold the check into the relevant request flavors; the
> "request < AP_DESTROY" check is just a bizarre way of implementing the
> AP_CREATE_ON_INIT => AP_CREATE fallthrough.
s/Oppurtunistically/Opportunistically/
Yes, with the change in patch #4 to not kick vCPUs on AP creation
failure, that check can now be moved to the switch statement.
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
>
> Fixes: e366f92ea99e ("KVM: SEV: Support SEV-SNP AP Creation NAE event")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/svm/sev.c | 23 ++++++++---------------
> 1 file changed, 8 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 07125b2cf0a6..8425198c5204 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3934,6 +3934,7 @@ void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu)
>
> static int sev_snp_ap_creation(struct vcpu_svm *svm)
> {
> + struct kvm_sev_info *sev = to_kvm_sev_info(svm->vcpu.kvm);
> struct kvm_vcpu *vcpu = &svm->vcpu;
> struct kvm_vcpu *target_vcpu;
> struct vcpu_svm *target_svm;
> @@ -3965,26 +3966,18 @@ static int sev_snp_ap_creation(struct vcpu_svm *svm)
>
> mutex_lock(&target_svm->sev_es.snp_vmsa_mutex);
>
> - /* Interrupt injection mode shouldn't change for AP creation */
> - if (request < SVM_VMGEXIT_AP_DESTROY) {
> - u64 sev_features;
> -
> - sev_features = vcpu->arch.regs[VCPU_REGS_RAX];
> - sev_features ^= to_kvm_sev_info(svm->vcpu.kvm)->vmsa_features;
> -
> - if (sev_features & SVM_SEV_FEAT_INT_INJ_MODES) {
> - vcpu_unimpl(vcpu, "vmgexit: invalid AP injection mode [%#lx] from guest\n",
> - vcpu->arch.regs[VCPU_REGS_RAX]);
> - ret = -EINVAL;
> - goto out;
> - }
> - }
> -
> switch (request) {
> case SVM_VMGEXIT_AP_CREATE_ON_INIT:
> kick = false;
> fallthrough;
> case SVM_VMGEXIT_AP_CREATE:
> + if (vcpu->arch.regs[VCPU_REGS_RAX] != sev->vmsa_features) {
> + vcpu_unimpl(vcpu, "vmgexit: mismatched AP sev_features [%#lx] != [%#llx] from guest\n",
> + vcpu->arch.regs[VCPU_REGS_RAX], sev->vmsa_features);
> + ret = -EINVAL;
> + goto out;
> + }
> +
> if (!page_address_valid(vcpu, svm->vmcb->control.exit_info_2)) {
> vcpu_unimpl(vcpu, "vmgexit: invalid AP VMSA address [%#llx] from guest\n",
> svm->vmcb->control.exit_info_2);