linux-kernel - [PATCH 07/10] KVM: x86: nSVM: Set vmcb02.g

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Message-ID: <20260113003016.3511895-8-jmattson@google.com>
Date: Mon, 12 Jan 2026 16:30:02 -0800
From: Jim Mattson <jmattson@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Shuah Khan <shuah@...nel.org>, Joerg Roedel <joro@...tes.org>, 
	Avi Kivity <avi@...hat.com>, Alexander Graf <agraf@...e.de>, 
	"Radim Krčmář" <rkrcmar@...hat.com>, David Hildenbrand <david@...nel.org>, Cathy Avery <cavery@...hat.com>, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Cc: Jim Mattson <jmattson@...gle.com>
Subject: [PATCH 07/10] KVM: x86: nSVM: Set vmcb02.g_pat correctly for nested NPT

When nested NPT is enabled in VMCB12, copy the (cached and validated)
VMCB12 g_pat field to the IA32_PAT MSR and to the VMCB02 g_pat
field. (The latter can be skipped if the VMCB02 g_pat field already
has the correct value.)

When NPT is enabled, but nested NPT is disabled, copy L1's IA32_PAT
MSR to the VMCB02 g_pat field (L1 and L2 share the same IA32_PAT MSR
in this scenario).

When NPT is disabled, the VMCB02 g_pat field is ignored by hardware.

Fixes: 15038e147247 ("KVM: SVM: obey guest PAT")
Signed-off-by: Jim Mattson <jmattson@...gle.com>
---
 arch/x86/kvm/svm/nested.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 501102625f69..90edea73ec58 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -656,9 +656,6 @@ 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;
@@ -666,6 +663,26 @@ 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)) {
+			/*
+			 * KVM doesn't implement a separate guest PAT
+			 * register. Instead, the guest PAT lives in
+			 * vcpu->arch.pat while in guest mode with
+			 * nested NPT enabled.
+			 */
+			vcpu->arch.pat = svm->nested.save.g_pat;
+			if (unlikely(new_vmcb12 ||
+				     vmcb_is_dirty(vmcb12, VMCB_NPT))) {
+				vmcb02->save.g_pat = svm->nested.save.g_pat;
+				vmcb_mark_dirty(vmcb02, VMCB_NPT);
+			}
+		} else {
+			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;
-- 
2.52.0.457.g6b5491de43-goog