Re: [PATCH v5 08/10] KVM: x86: nSVM: Save/restore gPAT with KVM_{GET,SET}_NESTED_STATE

[Jim Mattson]

On Wed, Mar 4, 2026 at 9:11 AM Sean Christopherson <sea...@google.com> wrote:
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 991ee4c03363..099bf8ac10ee 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1848,7 +1848,7 @@ static int svm_get_nested_state(struct kvm_vcpu *vcpu,
>         if (is_guest_mode(vcpu)) {
>                 kvm_state.hdr.svm.vmcb_pa = svm->nested.vmcb12_gpa;
>                 if (nested_npt_enabled(svm)) {
> -                       kvm_state.hdr.svm.flags |= KVM_STATE_SVM_VALID_GPAT;
> +                       kvm_state->flags |= KVM_STATE_NESTED_GPAT_VALID;
>                         kvm_state.hdr.svm.gpat = svm->vmcb->save.g_pat;
>                 }
>                 kvm_state.size += KVM_STATE_NESTED_SVM_VMCB_SIZE;
> @@ -1914,7 +1914,8 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>
>         if (kvm_state->flags & ~(KVM_STATE_NESTED_GUEST_MODE |
>                                  KVM_STATE_NESTED_RUN_PENDING |
> -                                KVM_STATE_NESTED_GIF_SET))
> +                                KVM_STATE_NESTED_GIF_SET |
> +                                KVM_STATE_NESTED_GPAT_VALID))
>                 return -EINVAL;

Unless I'm missing something, this breaks forward compatibility
completely. An older kernel will refuse to accept a nested state blob
with GPAT_VALID set.