KVM: x86/xen: latch long_mode when hypercall page is set up

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

include/uapi/linux/kvm.h

@@ -1594,10 +1594,13 @@ struct kvm_xen_hvm_attr {
 	__u16 type;
 	__u16 pad[3];
 	union {
+		__u8 long_mode;
 		__u64 pad[8];
 	} u;
 };
 
+#define KVM_XEN_ATTR_TYPE_LONG_MODE		0x0
+
 /* Secure Encrypted Virtualization command */
 enum sev_cmd_id {
 	/* Guest initialization commands */