February 6, 2026 at 10:23 AM, "Sean Christopherson" <[email protected]> wrote: > > On Thu, Feb 05, 2026, Jim Mattson wrote: > > > > > When nested NPT is enabled in vmcb12, copy the (cached and validated) > > vmcb12 g_pat field to the guest PAT register. Under KVM, the guest PAT > > register lives in the vmcb02 g_pat field. > > > > When NPT is enabled, but nested NPT is disabled, copy L1's IA32_PAT MSR to > > the vmcb02 g_pat field, since L2 shares the IA32_PAT MSR with L1. > > > > When NPT is disabled, the vmcb02 g_pat field is ignored by hardware. > > > Uber nit, the "vmcb02" qualifier can be dropped, i.e. > > When NPT is disabled, the g_pat field is ignored by hardware. > > Scoping it to vmcb02 makes it sound like there's a special rule about vmcb02. > > > > > Fixes: 15038e147247 ("KVM: SVM: obey guest PAT") > > Signed-off-by: Jim Mattson <[email protected]> > > --- > > arch/x86/kvm/svm/nested.c | 16 +++++++++++++--- > > 1 file changed, 13 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c > > index 1d4ff6408b34..1ff2ede96094 100644 > > --- a/arch/x86/kvm/svm/nested.c > > +++ b/arch/x86/kvm/svm/nested.c > > @@ -646,9 +646,6 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm > > *svm, struct vmcb *vmcb12 > > struct vmcb *vmcb02 = svm->nested.vmcb02.ptr; > > struct kvm_vcpu *vcpu = &svm->vcpu; > > > > - nested_vmcb02_compute_g_pat(svm); > > - vmcb_mark_dirty(vmcb02, VMCB_NPT); > > - > > /* Load the nested guest state */ > > if (svm->nested.vmcb12_gpa != svm->nested.last_vmcb12_gpa) { > > new_vmcb12 = true; > > @@ -656,6 +653,19 @@ static void nested_vmcb02_prepare_save(struct > > vcpu_svm *svm, struct vmcb *vmcb12 > > svm->nested.force_msr_bitmap_recalc = true; > > } > > > > + if (npt_enabled) { > > + if (nested_npt_enabled(svm)) { > > + if (unlikely(new_vmcb12 || > > + vmcb_is_dirty(vmcb12, VMCB_NPT))) { > > + vmcb02->save.g_pat = svm->nested.gpat; > > + vmcb_mark_dirty(vmcb02, VMCB_NPT); > > + } > > + } else { > > + vmcb02->save.g_pat = vcpu->arch.pat; > > + vmcb_mark_dirty(vmcb02, VMCB_NPT); > > + } > > + } > > > To reduce indentation, how about this? There's a consistency check for > nested_npt_enabled() vs. npt_enabled, so it's guaranteed to do the right > thing.
You mean the one that goes away after this patch: https://lore.kernel.org/kvm/[email protected]/? > > if (nested_npt_enabled(svm)) { > if (unlikely(new_vmcb12 || vmcb_is_dirty(vmcb12, VMCB_NPT))) { > vmcb02->save.g_pat = svm->nested.gpat; > vmcb_mark_dirty(vmcb02, VMCB_NPT); > } > } else if (npt_enabled) { > vmcb02->save.g_pat = vcpu->arch.pat; > vmcb_mark_dirty(vmcb02, VMCB_NPT); > } > > > > > + > > if (unlikely(new_vmcb12 || vmcb_is_dirty(vmcb12, VMCB_SEG))) { > > vmcb02->save.es = vmcb12->save.es; > > vmcb02->save.cs = vmcb12->save.cs; > > -- > > 2.53.0.rc2.204.g2597b5adb4-goog > > >
