[PATCH 04/10] KVM: x86: nSVM: Restore L1's PAT on emulated #VMEXIT from L2 to L1

[Jim Mattson]

KVM doesn't implement a separate G_PAT register to hold the guest's
PAT in guest mode with nested NPT enabled. Consequently, L1's IA32_PAT
MSR must be restored on emulated #VMEXIT from L2 to L1.

Note: if L2 uses shadow paging, L1 and L2 share the same IA32_PAT MSR.

Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
---
 arch/x86/kvm/svm/nested.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index c751be470364..9aec836ac04c 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1292,6 +1292,16 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	kvm_rsp_write(vcpu, vmcb01->save.rsp);
 	kvm_rip_write(vcpu, vmcb01->save.rip);
 
+	/*
+	 * 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. Hence, the
+	 * IA32_PAT MSR has to be restored from the vmcb01 g_pat at
+	 * #VMEXIT.
+	 */
+	if (nested_npt_enabled(svm))
+		vcpu->arch.pat = vmcb01->save.g_pat;
+
 	svm->vcpu.arch.dr7 = DR7_FIXED_1;
 	kvm_update_dr7(&svm->vcpu);
 
-- 
2.52.0.457.g6b5491de43-goog