linux-kernel - [RFC PATCH 3/6] KVM: x86: nSVM: Copy current vmcb02 g_pat to vmcb12 g

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Message-ID: <20251107201151.3303170-4-jmattson@google.com>
Date: Fri,  7 Nov 2025 12:11:26 -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>, Alexander Graf <agraf@...e.de>, Joerg Roedel <joro@...tes.org>, 
	Avi Kivity <avi@...hat.com>, 
	"Radim Krčmář" <rkrcmar@...hat.com>, David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Cc: Jim Mattson <jmattson@...gle.com>
Subject: [RFC PATCH 3/6] KVM: x86: nSVM: Copy current vmcb02 g_pat to vmcb12
 g_pat on #VMEXIT

According to the APM volume 3 pseudo-code for "VMRUN," when nested
paging is enabled in the VMCB, the guest PAT register is copied into
the g_pat field of the VMCB on #VMEXIT.

In KVM, the guest PAT register is the g_pat field of vmcb02. When
nested paging is enabled in vmcb12, copy the g_pat field of the vmcb02
to the g_pat field of the vmcb12 in nested_svm_vmexit().

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

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index c68511948501..51a89d6aa29f 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1126,6 +1126,9 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	vmcb12->save.dr6    = svm->vcpu.arch.dr6;
 	vmcb12->save.cpl    = vmcb02->save.cpl;
 
+	if (nested_npt_enabled(svm))
+		vmcb12->save.g_pat = vmcb02->save.g_pat;
+
 	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK)) {
 		vmcb12->save.s_cet	= vmcb02->save.s_cet;
 		vmcb12->save.isst_addr	= vmcb02->save.isst_addr;
-- 
2.51.2.1041.gc1ab5b90ca-goog