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

Jim Mattson
2026-04-07T03:08:39Z

On Mon, Apr 6, 2026 at 4:47 PM Sean Christopherson <seanjc@google.com> 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
> >