KVM: VMX: Save HOST_CR3 in vmx_prepare_switch_to_guest()

The host CR3 in the vcpu thread can only be changed when scheduling.
Moving the code in vmx_prepare_switch_to_guest() makes the code
simpler.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20211118110814.2568-5-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -3033,7 +3033,7 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
 static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
-	unsigned long cr3, cr4;
+	unsigned long cr4;
 	bool vm_fail;
 
 	if (!nested_early_check)
@@ -3056,12 +3056,6 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
 	 */
 	vmcs_writel(GUEST_RFLAGS, 0);
 
-	cr3 = __get_current_cr3_fast();
-	if (unlikely(cr3 != vmx->loaded_vmcs->host_state.cr3)) {
-		vmcs_writel(HOST_CR3, cr3);
-		vmx->loaded_vmcs->host_state.cr3 = cr3;
-	}
-
 	cr4 = cr4_read_shadow();
 	if (unlikely(cr4 != vmx->loaded_vmcs->host_state.cr4)) {
 		vmcs_writel(HOST_CR4, cr4);

arch/x86/kvm/vmx/vmx.c

@@ -1103,6 +1103,7 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 #ifdef CONFIG_X86_64
 	int cpu = raw_smp_processor_id();
 #endif
+	unsigned long cr3;
 	unsigned long fs_base, gs_base;
 	u16 fs_sel, gs_sel;
 	int i;
@@ -1167,6 +1168,14 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 #endif
 
 	vmx_set_host_fs_gs(host_state, fs_sel, gs_sel, fs_base, gs_base);
+
+	/* Host CR3 including its PCID is stable when guest state is loaded. */
+	cr3 = __get_current_cr3_fast();
+	if (unlikely(cr3 != host_state->cr3)) {
+		vmcs_writel(HOST_CR3, cr3);
+		host_state->cr3 = cr3;
+	}
+
 	vmx->guest_state_loaded = true;
 }
 
@@ -6612,7 +6621,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
-	unsigned long cr3, cr4;
+	unsigned long cr4;
 
 	/* Record the guest's net vcpu time for enforced NMI injections. */
 	if (unlikely(!enable_vnmi &&
@@ -6657,12 +6666,6 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
 		vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
 	vcpu->arch.regs_dirty = 0;
 
-	cr3 = __get_current_cr3_fast();
-	if (unlikely(cr3 != vmx->loaded_vmcs->host_state.cr3)) {
-		vmcs_writel(HOST_CR3, cr3);
-		vmx->loaded_vmcs->host_state.cr3 = cr3;
-	}
-
 	cr4 = cr4_read_shadow();
 	if (unlikely(cr4 != vmx->loaded_vmcs->host_state.cr4)) {
 		vmcs_writel(HOST_CR4, cr4);