KVM: nVMX: fix vmentry failure code when L2 state would require emulation

Commit 2bb8cafe ("KVM: vVMX: signal failure for nested VMEntry if
emulation_required", 2018-03-12) introduces a new error path which does
not set *entry_failure_code.  Fix that to avoid a leak of L0 stack to L1.
Reported-by: NRadim Krčmář <rkrcmar@redhat.com>
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx.c

@@ -11059,8 +11059,10 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 	 * which means L1 attempted VMEntry to L2 with invalid state.
 	 * Fail the VMEntry.
 	 */
-	if (vmx->emulation_required)
+	if (vmx->emulation_required) {
+		*entry_failure_code = ENTRY_FAIL_DEFAULT;
 		return 1;
+	}
 
 	/* Shadow page tables on either EPT or shadow page tables. */
 	if (nested_vmx_load_cr3(vcpu, vmcs12->guest_cr3, nested_cpu_has_ept(vmcs12),