linux-kernel - [RFC PATCH 6/6] KVM: x86: nSVM: Use cached VMCB12 g

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Message-ID: <20251107201151.3303170-7-jmattson@google.com>
Date: Fri,  7 Nov 2025 12:11:29 -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 6/6] KVM: x86: nSVM: Use cached VMCB12 g_pat in VMCB02
 when using NPT

When nested paging is enabled in VMCB12, copy the (cached and
validated) VMCB12 g_pat to VMCB02.

Fixes: 15038e147247 ("KVM: SVM: obey guest PAT")
Signed-off-by: Jim Mattson <jmattson@...gle.com>
---
 arch/x86/kvm/svm/nested.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 43429399993c..21d8db10525d 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -605,8 +605,10 @@ void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm)
 	if (!svm->nested.vmcb02.ptr)
 		return;
 
-	/* FIXME: merge g_pat from vmcb01 and vmcb12.  */
-	svm->nested.vmcb02.ptr->save.g_pat = svm->vmcb01.ptr->save.g_pat;
+	if (nested_npt_enabled(svm))
+		svm->nested.vmcb02.ptr->save.g_pat = svm->nested.ctl.g_pat;
+	else
+		svm->nested.vmcb02.ptr->save.g_pat = svm->vmcb01.ptr->save.g_pat;
 }
 
 static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12)
-- 
2.51.2.1041.gc1ab5b90ca-goog