kvm: nVMX: Reorder error checks for emulated VMXON

Checks on the operand to VMXON are performed after the check for
legacy mode operation and the #GP checks, according to the pseudo-code
in Intel's SDM.

Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/vmx.c

@@ -7180,9 +7180,6 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
 		return 1;
 	}
 
-	if (nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMON, NULL))
-		return 1;
-
 	if (vmx->nested.vmxon) {
 		nested_vmx_failValid(vcpu, VMXERR_VMXON_IN_VMX_ROOT_OPERATION);
 		return kvm_skip_emulated_instruction(vcpu);
@@ -7194,6 +7191,9 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
 		return 1;
 	}
 
+	if (nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMON, NULL))
+		return 1;
+
 	if (cpu_has_vmx_msr_bitmap()) {
 		vmx->nested.msr_bitmap =
 				(unsigned long *)__get_free_page(GFP_KERNEL);