On Thu, Feb 12, 2026 at 07:58:51AM -0800, Jim Mattson wrote:
> When nested NPT is enabled in vmcb12, copy the (cached and validated)
> vmcb12 g_pat field to the guest PAT register. Under KVM, the guest PAT
> register lives in svm->nested.save.g_pat.
>
> When NPT is enabled, but nested NPT is disabled, copy L1's IA32_PAT MSR to
> the vmcb02 g_pat field, since L2 shares the IA32_PAT MSR with L1.
>
> When NPT is disabled, the g_pat field is ignored by hardware.
>
> Fixes: 15038e147247 ("KVM: SVM: obey guest PAT")
> Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> ---
> arch/x86/kvm/svm/nested.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 91b35adb83f8..dc8275837120 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -724,9 +724,6 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm)
> struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
> struct kvm_vcpu *vcpu = &svm->vcpu;
>
> - nested_vmcb02_compute_g_pat(svm);
> - vmcb_mark_dirty(vmcb02, VMCB_NPT);
> -
> /* Load the nested guest state */
> if (svm->nested.vmcb12_gpa != svm->nested.last_vmcb12_gpa) {
> new_vmcb12 = true;
> @@ -757,6 +754,13 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm)
> vmcb_mark_dirty(vmcb02, VMCB_CET);
> }
>
> + if (nested_npt_enabled(svm)) {
> + if (unlikely(new_vmcb12 || vmcb12_is_dirty(control, VMCB_NPT)))
> + vmcb_set_gpat(vmcb02, svm->nested.save.g_pat);
> + } else if (npt_enabled) {
> + vmcb_set_gpat(vmcb02, vcpu->arch.pat);
> + }
> +
> kvm_set_rflags(vcpu, save->rflags | X86_EFLAGS_FIXED);
>
> svm_set_efer(vcpu, svm->nested.save.efer);
> --
> 2.53.0.239.g8d8fc8a987-goog
>