On Mon, Jan 12, 2026, Jim Mattson wrote:
> KVM doesn't implement a separate G_PAT register to hold the guest's
> PAT in guest mode with nested NPT enabled. Consequently, L1's IA32_PAT
> MSR must be restored on emulated #VMEXIT from L2 to L1.
>
> Note: if L2 uses shadow paging, L1 and L2 share the same IA32_PAT MSR.
>
> Signed-off-by: Jim Mattson <jmattson@google.com>
> ---
> arch/x86/kvm/svm/nested.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index c751be470364..9aec836ac04c 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1292,6 +1292,16 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
> kvm_rsp_write(vcpu, vmcb01->save.rsp);
> kvm_rip_write(vcpu, vmcb01->save.rip);
>
> + /*
> + * KVM doesn't implement a separate guest PAT
> + * register. Instead, the guest PAT lives in vcpu->arch.pat
> + * while in guest mode with nested NPT enabled. Hence, the
> + * IA32_PAT MSR has to be restored from the vmcb01 g_pat at
> + * #VMEXIT.
Wrap closer to 80 chars.
> + */
> + if (nested_npt_enabled(svm))
> + vcpu->arch.pat = vmcb01->save.g_pat;
> +
> svm->vcpu.arch.dr7 = DR7_FIXED_1;
> kvm_update_dr7(&svm->vcpu);
>
> --
> 2.52.0.457.g6b5491de43-goog
>