Re: [PATCH v5 05/10] KVM: x86: nSVM: Redirect IA32_PAT accesses to either hPAT or gPAT

[Yosry Ahmed]

On Tue, Feb 24, 2026 at 9:43 AM Sean Christopherson <sea...@google.com> wrote:
>
> On Mon, Feb 23, 2026, Jim Mattson wrote:
> > +static void svm_set_pat(struct kvm_vcpu *vcpu, bool from_host, u64 data)
> > +{
> > +     struct vcpu_svm *svm = to_svm(vcpu);
> > +
> > +     if (svm_pat_accesses_gpat(vcpu, from_host)) {
> > +             vmcb_set_gpat(svm->vmcb, data);
> > +     } else {
> > +             svm->vcpu.arch.pat = data;
> > +             if (npt_enabled) {
> > +                     vmcb_set_gpat(svm->vmcb01.ptr, data);
> > +                     if (is_guest_mode(&svm->vcpu) &&
> > +                         !nested_npt_enabled(svm))
> > +                             vmcb_set_gpat(svm->vmcb, data);
> > +             }
> > +     }
>
> Overall, this LGTM.  For this particular code, any objection to using early
> returns to reduce indentation?  The else branch above is a bit gnarly, 
> especially
> when legacy_gpat_semantics comes along.
>
> I.e. end up with this
>
>   static void svm_set_pat(struct kvm_vcpu *vcpu, bool from_host, u64 data)
>   {
>         struct vcpu_svm *svm = to_svm(vcpu);
>
>         if (svm_pat_accesses_gpat(vcpu, from_host)) {
>                 vmcb_set_gpat(svm->vmcb, data);
>                 return;
>         }
>
>         svm->vcpu.arch.pat = data;
>
>         if (!npt_enabled)
>                 return;
>
>         vmcb_set_gpat(svm->vmcb01.ptr, data);
>         if (is_guest_mode(&svm->vcpu) &&
>             (svm->nested.legacy_gpat_semantics || !nested_npt_enabled(svm)))
>                 vmcb_set_gpat(svm->vmcb, data);
>   }
>
> I can fixup when applying (unless you and/or Yosry object).

LGTM.