linux-kernel - [RFC PATCH 4/6] KVM: x86: nSVM: Cache g_pat in vmcb_ctrl_area

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Message-ID: <20251107201151.3303170-5-jmattson@google.com>
Date: Fri,  7 Nov 2025 12:11:27 -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 4/6] KVM: x86: nSVM: Cache g_pat in vmcb_ctrl_area_cached

Add a g_pat field to the vmcb_ctrl_area_cached struct for caching the
VMCB12 g_pat at emulated VMRUN. This is a preliminary step to allow
for proper validation and handling of the VMCB12 g_pat when nested
paging is enabled in VMCB12.

Fixes: 3d6368ef580a ("KVM: SVM: Add VMRUN handler")
Signed-off-by: Jim Mattson <jmattson@...gle.com>
---
 arch/x86/kvm/svm/nested.c | 6 ++++++
 arch/x86/kvm/svm/svm.h    | 1 +
 2 files changed, 7 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 51a89d6aa29f..6e48572e2bd7 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -984,6 +984,12 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 
 	nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
 	nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
+	/*
+	 * To facilitate independent validation of the cached state
+	 * save area and the cached control area, we cache the vmcb12
+	 * g_pat with the cached controls.
+	 */
+	svm->nested.ctl.g_pat = vmcb12->save.g_pat;
 
 	if (!nested_vmcb_check_save(vcpu) ||
 	    !nested_vmcb_check_controls(vcpu)) {
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index e4b04f435b3d..c91e20aa3ec2 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -176,6 +176,7 @@ struct vmcb_ctrl_area_cached {
 	u64 virt_ext;
 	u32 clean;
 	u64 bus_lock_rip;
+	u64 g_pat;
 	union {
 #if IS_ENABLED(CONFIG_HYPERV) || IS_ENABLED(CONFIG_KVM_HYPERV)
 		struct hv_vmcb_enlightenments hv_enlightenments;
-- 
2.51.2.1041.gc1ab5b90ca-goog