linux-kernel - [PATCH v3 6/8] KVM: x86: nSVM: Save/restore gPAT with KVM_{GET,SET}_NESTED

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Message-ID: <20260205214326.1029278-7-jmattson@google.com>
Date: Thu,  5 Feb 2026 13:43:06 -0800
From: Jim Mattson <jmattson@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Thomas Gleixner <tglx@...nel.org>, 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>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Jim Mattson <jmattson@...gle.com>
Subject: [PATCH v3 6/8] KVM: x86: nSVM: Save/restore gPAT with KVM_{GET,SET}_NESTED_STATE

Add a 'flags' field to the SVM nested state header, and use bit 0 of the
flags to indicate that gPAT is stored in the nested state.

If in guest mode with NPT enabled, store the current vmcb->save.g_pat value
into the header of the nested state, and set the flag.

Note that struct kvm_svm_nested_state_hdr is included in a union padded to
120 bytes, so there is room to add the flags field and the gpt field
without changing any offsets.

Fixes: cc440cdad5b7 ("KVM: nSVM: implement KVM_GET_NESTED_STATE and KVM_SET_NESTED_STATE")
Signed-off-by: Jim Mattson <jmattson@...gle.com>
---
 arch/x86/include/uapi/asm/kvm.h |  5 +++++
 arch/x86/kvm/svm/nested.c       | 14 ++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 846a63215ce1..664d04d1db3f 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -495,6 +495,8 @@ struct kvm_sync_regs {
 
 #define KVM_STATE_VMX_PREEMPTION_TIMER_DEADLINE	0x00000001
 
+#define KVM_STATE_SVM_VALID_GPAT	0x00000001
+
 /* vendor-independent attributes for system fd (group 0) */
 #define KVM_X86_GRP_SYSTEM		0
 #  define KVM_X86_XCOMP_GUEST_SUPP	0
@@ -531,6 +533,9 @@ struct kvm_svm_nested_state_data {
 
 struct kvm_svm_nested_state_hdr {
 	__u64 vmcb_pa;
+	__u32 flags;
+	__u32 reserved;
+	__u64 gpat;
 };
 
 /* for KVM_CAP_NESTED_STATE */
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 0b95ae1e864b..3f512fb630db 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1764,6 +1764,10 @@ static int svm_get_nested_state(struct kvm_vcpu *vcpu,
 	/* First fill in the header and copy it out.  */
 	if (is_guest_mode(vcpu)) {
 		kvm_state.hdr.svm.vmcb_pa = svm->nested.vmcb12_gpa;
+		if (nested_npt_enabled(svm)) {
+			kvm_state.hdr.svm.flags |= KVM_STATE_SVM_VALID_GPAT;
+			kvm_state.hdr.svm.gpat = svm->nested.gpat;
+		}
 		kvm_state.size += KVM_STATE_NESTED_SVM_VMCB_SIZE;
 		kvm_state.flags |= KVM_STATE_NESTED_GUEST_MODE;
 
@@ -1889,6 +1893,12 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	    !__nested_vmcb_check_save(vcpu, &save_cached))
 		goto out_free;
 
+	/*
+	 * Validate gPAT, if provided.
+	 */
+	if ((kvm_state->hdr.svm.flags & KVM_STATE_SVM_VALID_GPAT) &&
+	    !kvm_pat_valid(kvm_state->hdr.svm.gpat))
+		goto out_free;
 
 	/*
 	 * All checks done, we can enter guest mode. Userspace provides
@@ -1926,6 +1936,10 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	if (ret)
 		goto out_free;
 
+	if (nested_npt_enabled(svm) &&
+	    (kvm_state->hdr.svm.flags & KVM_STATE_SVM_VALID_GPAT))
+		svm_set_gpat(svm, kvm_state->hdr.svm.gpat);
+
 	svm->nested.force_msr_bitmap_recalc = true;
 
 	kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
-- 
2.53.0.rc2.204.g2597b5adb4-goog