Re: [PATCH v7 8/9] KVM: x86: nSVM: Save/restore gPAT with KVM_{GET,SET}_NESTED_STATE

[Jim Mattson]

On Mon, Apr 6, 2026 at 4:47 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Fri, Mar 27, 2026, Jim Mattson wrote:
> > @@ -1918,6 +1921,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> >       struct vmcb_save_area_cached save_cached;
> >       struct vmcb_ctrl_area_cached ctl_cached;
> >       unsigned long cr0;
> > +     bool use_separate_l2_pat;
>
> Land this above "cr0" to preserve the inverted fir tree.
>
> >       int ret;
> >
> >       BUILD_BUG_ON(sizeof(struct vmcb_control_area) + sizeof(struct vmcb_save_area) >
> > @@ -1993,6 +1997,18 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> >           !nested_vmcb_check_save(vcpu, &save_cached, false))
> >               goto out_free;
> >
> > +     /*
> > +      * Validate gPAT when the shared PAT quirk is disabled (i.e. L2
> > +      * has its own gPAT). This is done separately from the
> > +      * vmcb_save_area_cached validation above, because gPAT is L2
> > +      * state, but the vmcb_save_area_cached is populated with L1 state.
> > +      */
> > +     use_separate_l2_pat =
> > +             (ctl_cached.misc_ctl & SVM_MISC_ENABLE_NP) &&
> > +             !kvm_check_has_quirk(vcpu->kvm,
> > +                                  KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT);
>
> I vote for either:
>
>         use_separate_l2_pat = (ctl_cached.misc_ctl & SVM_MISC_ENABLE_NP) &&
>                               !kvm_check_has_quirk(vcpu->kvm,
>                                                    KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT);
>
LOL! Aren't you the one who keeps complaining that my indentation
doesn't line up? Are you schizophrenic?

> or
>
>         use_separate_l2_pat = (ctl_cached.misc_ctl & SVM_MISC_ENABLE_NP);
>         if (kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT))
>                 use_separate_l2_pat = false;

Wow. I really have no idea how to predict what you're going to want
the code to look like. How is this better than the original?!?

>
> > +     if (use_separate_l2_pat && !kvm_pat_valid(kvm_state->hdr.svm.gpat))
> > +             goto out_free;
> >
> >       /*
> >        * All checks done, we can enter guest mode. Userspace provides
> > @@ -2017,6 +2033,10 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> >       nested_copy_vmcb_control_to_cache(svm, ctl);
> >
> >       svm_switch_vmcb(svm, &svm->nested.vmcb02);
> > +
> > +     if (use_separate_l2_pat)
> > +             vmcb_set_gpat(svm->vmcb, kvm_state->hdr.svm.gpat);
> > +
> >       nested_vmcb02_prepare_control(svm);
> >
> >       /*
> > --
> > 2.53.0.1018.g2bb0e51243-goog
> >