[PATCH 25/43] KVM: nVMX: Update vmcs12 for MSR_IA32_CR_PAT when it's written

[Paolo Bonzini]

From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

As alluded to by the TODO comment, KVM unconditionally intercepts writes
to the PAT MSR.  In the unlikely event that L1 allows L2 to write L1's
PAT directly but saves L2's PAT on VM-Exit, update vmcs12 when L2 writes
the PAT.  This eliminates the need to VMREAD the value from vmcs02 on
VM-Exit as vmcs12 is already up to date in all situations.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/nested.c | 4 ----
 arch/x86/kvm/vmx/vmx.c    | 4 ++++
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index a012118e6c8c..4a91a86b5f0a 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3564,10 +3564,6 @@ static void sync_vmcs02_to_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 		vmcs12->guest_ia32_debugctl = vmcs_read64(GUEST_IA32_DEBUGCTL);
 	}
 
-	/* TODO: These cannot have changed unless we have MSR bitmaps and
-	 * the relevant bit asks not to trap the change */
-	if (vmcs12->vm_exit_controls & VM_EXIT_SAVE_IA32_PAT)
-		vmcs12->guest_ia32_pat = vmcs_read64(GUEST_IA32_PAT);
 	if (vmcs12->vm_exit_controls & VM_EXIT_SAVE_IA32_EFER)
 		vmcs12->guest_ia32_efer = vcpu->arch.efer;
 	vmcs12->guest_sysenter_cs = vmcs_read32(GUEST_SYSENTER_CS);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 7a2d9a4b828c..56783060449d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1910,6 +1910,10 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (!kvm_pat_valid(data))
 			return 1;
 
+		if (is_guest_mode(vcpu) &&
+		    get_vmcs12(vcpu)->vm_exit_controls & VM_EXIT_SAVE_IA32_PAT)
+			get_vmcs12(vcpu)->guest_ia32_pat = data;
+
 		if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) {
 			vmcs_write64(GUEST_IA32_PAT, data);
 			vcpu->arch.pat = data;
-- 
1.8.3.1