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Peter Anvin" , Shuah Khan , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Yosry Ahmed Content-Type: text/plain; charset="us-ascii" On Mon, Feb 23, 2026, Jim Mattson wrote: > @@ -2075,9 +2076,15 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, > > svm_switch_vmcb(svm, &svm->nested.vmcb02); > > - if (nested_npt_enabled(svm) && > - (kvm_state->hdr.svm.flags & KVM_STATE_SVM_VALID_GPAT)) > - vmcb_set_gpat(svm->vmcb, kvm_state->hdr.svm.gpat); > + svm->nested.legacy_gpat_semantics = > + nested_npt_enabled(svm) && > + !(kvm_state->hdr.svm.flags & KVM_STATE_SVM_VALID_GPAT); > + if (nested_npt_enabled(svm)) { > + u64 g_pat = svm->nested.legacy_gpat_semantics ? > + vcpu->arch.pat : kvm_state->hdr.svm.gpat; This is all a bit gnarly, e.g. the indentation and wrapping, as well as the logic (not that it's wrong, just a bit hard to follow the chain of events). Rather than set legacy_gpat_semantics directly, what if we clear it by default, and then set it %true in the exact path where KVM uses legacy semantics. svm->nested.legacy_gpat_semantics = false; if (nested_npt_enabled(svm)) { if (kvm_state->hdr.svm.flags & KVM_STATE_SVM_VALID_GPAT) { vmcb_set_gpat(svm->vmcb, kvm_state->hdr.svm.gpat); } else { svm->nested.legacy_gpat_semantics = true; vmcb_set_gpat(svm->vmcb, vcpu->arch.pat); } } As a bonus, if the previous patch is deliberately "bad" and does: if (nested_npt_enabled(svm)) { if (kvm_state->hdr.svm.flags & KVM_STATE_SVM_VALID_GPAT) vmcb_set_gpat(svm->vmcb, kvm_state->hdr.svm.gpat); } then the diff for this snippet shrinks to: @@ -2025,9 +2026,14 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, svm_switch_vmcb(svm, &svm->nested.vmcb02); + svm->nested.legacy_gpat_semantics = false; if (nested_npt_enabled(svm)) { - if (kvm_state->hdr.svm.flags & KVM_STATE_SVM_VALID_GPAT) + if (kvm_state->hdr.svm.flags & KVM_STATE_SVM_VALID_GPAT) { vmcb_set_gpat(svm->vmcb, kvm_state->hdr.svm.gpat); + } else { + svm->nested.legacy_gpat_semantics = true; + vmcb_set_gpat(svm->vmcb, vcpu->arch.pat); + } } nested_vmcb02_prepare_control(svm); > + > + vmcb_set_gpat(svm->nested.vmcb02.ptr, g_pat); I don't like the switch from svm->vmcb to svm->nested.vmcb02.ptr. For better or worse, the existing code uses svm->vmcb, so I think it makes sense to use that. If we want to explicitly use vmcb02, then we should capture svm->nested.vmcb02.ptr locally as vmcb02 (in a future cleanup patch). > + } > > nested_vmcb02_prepare_control(svm, svm->vmcb->save.rip, svm->vmcb->save.cs.base); > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index 00dba10991a5..ac45702f566e 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -2727,7 +2727,8 @@ static bool svm_pat_accesses_gpat(struct kvm_vcpu *vcpu, bool from_host) > * with older kernels. > */ > WARN_ON_ONCE(from_host && vcpu->wants_to_run); > - return !from_host && is_guest_mode(vcpu) && nested_npt_enabled(svm); > + return !svm->nested.legacy_gpat_semantics && !from_host && > + is_guest_mode(vcpu) && nested_npt_enabled(svm); Align indentation (it's a shame return wasn't spelled retturn, it would save many spaces).