x86/KVM/nVMX: don't use clean fields data on enlightened VMLAUNCH

Apparently, Windows doesn't maintain clean fields data after it does
VMCLEAR for an enlightened VMCS so we can only use it on VMRESUME.
The issue went unnoticed because currently we do nested_release_evmcs()
in handle_vmclear() and the consecutive enlightened VMPTRLD invalidates
clean fields when a new eVMCS is mapped but we're going to change the
logic.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -1784,6 +1784,7 @@ static int nested_vmx_handle_enlightened_vmptrld(struct kvm_vcpu *vcpu,
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	struct hv_vp_assist_page assist_page;
+	bool evmcs_gpa_changed = false;
 
 	if (likely(!vmx->nested.enlightened_vmcs_enabled))
 		return 1;
@@ -1837,15 +1838,9 @@ static int nested_vmx_handle_enlightened_vmptrld(struct kvm_vcpu *vcpu,
 		}
 
 		vmx->nested.dirty_vmcs12 = true;
-		/*
-		 * As we keep L2 state for one guest only 'hv_clean_fields' mask
-		 * can't be used when we switch between them. Reset it here for
-		 * simplicity.
-		 */
-		vmx->nested.hv_evmcs->hv_clean_fields &=
-			~HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
 		vmx->nested.hv_evmcs_vmptr = assist_page.current_nested_vmcs;
 
+		evmcs_gpa_changed = true;
 		/*
 		 * Unlike normal vmcs12, enlightened vmcs12 is not fully
 		 * reloaded from guest's memory (read only fields, fields not
@@ -1859,6 +1854,15 @@ static int nested_vmx_handle_enlightened_vmptrld(struct kvm_vcpu *vcpu,
 		}
 
 	}
+
+	/*
+	 * Clean fields data can't de used on VMLAUNCH and when we switch
+	 * between different L2 guests as KVM keeps a single VMCS12 per L1.
+	 */
+	if (from_launch || evmcs_gpa_changed)
+		vmx->nested.hv_evmcs->hv_clean_fields &=
+			~HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
+
 	return 1;
 }
 
@@ -3092,7 +3096,7 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 	if (!nested_vmx_check_permission(vcpu))
 		return 1;
 
-	if (!nested_vmx_handle_enlightened_vmptrld(vcpu, true))
+	if (!nested_vmx_handle_enlightened_vmptrld(vcpu, launch))
 		return 1;
 
 	if (!vmx->nested.hv_evmcs && vmx->nested.current_vmptr == -1ull)