February 6, 2026 at 10:19 AM, "Sean Christopherson" <[email protected]> wrote:
>
> On Thu, Feb 05, 2026, Jim Mattson wrote:
>
> >
> > Cache g_pat from vmcb12 in svm->nested.gpat to avoid TOCTTOU issues, and
> > add a validity check so that when nested paging is enabled for vmcb12, an
> > invalid g_pat causes an immediate VMEXIT with exit code VMEXIT_INVALID, as
> > specified in the APM, volume 2: "Nested Paging and VMRUN/VMEXIT."
> >
> > Fixes: 3d6368ef580a ("KVM: SVM: Add VMRUN handler")
> > Signed-off-by: Jim Mattson <[email protected]>
> > ---
> > arch/x86/kvm/svm/nested.c | 4 +++-
> > arch/x86/kvm/svm/svm.h | 3 +++
> > 2 files changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> > index f72dbd10dcad..1d4ff6408b34 100644
> > --- a/arch/x86/kvm/svm/nested.c
> > +++ b/arch/x86/kvm/svm/nested.c
> > @@ -1027,9 +1027,11 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
> >
> > nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
> > nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
> > + svm->nested.gpat = vmcb12->save.g_pat;
> >
> > if (!nested_vmcb_check_save(vcpu) ||
> > - !nested_vmcb_check_controls(vcpu)) {
> > + !nested_vmcb_check_controls(vcpu) ||
> > + (nested_npt_enabled(svm) && !kvm_pat_valid(svm->nested.gpat))) {
> > vmcb12->control.exit_code = SVM_EXIT_ERR;
> > vmcb12->control.exit_info_1 = 0;
> > vmcb12->control.exit_info_2 = 0;
> > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> > index 986d90f2d4ca..42a4bf83b3aa 100644
> > --- a/arch/x86/kvm/svm/svm.h
> > +++ b/arch/x86/kvm/svm/svm.h
> > @@ -208,6 +208,9 @@ struct svm_nested_state {
> > */
> > struct vmcb_save_area_cached save;
> >
> > + /* Cached guest PAT from vmcb12.save.g_pat */
> > + u64 gpat;
> >
> Shouldn't this go in vmcb_save_area_cached?
I believe Jim changed it after this discussion on v2:
https://lore.kernel.org/kvm/[email protected]/.
