KVM: hide KVM_MEMSLOT_INVALID from userspace

Quote Avi's comment:
| KVM_MEMSLOT_INVALID is actually an internal symbol, not used by
| userspace.  Please move it to kvm_host.h.

Also, we divide the memlsot->flags into two parts, the lower 16 bits
are visible for userspace, the higher 16 bits are internally used in
kvm

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

include/linux/kvm.h

@@ -101,9 +101,12 @@ struct kvm_userspace_memory_region {
 	__u64 userspace_addr; /* start of the userspace allocated memory */
 };
 
-/* for kvm_memory_region::flags */
+/*
+ * The bit 0 ~ bit 15 of kvm_memory_region::flags are visible for userspace,
+ * other bits are reserved for kvm internal use which are defined in
+ * include/linux/kvm_host.h.
+ */
 #define KVM_MEM_LOG_DIRTY_PAGES  1UL
-#define KVM_MEMSLOT_INVALID      (1UL << 1)
 
 /* for KVM_IRQ_LINE */
 struct kvm_irq_level {

include/linux/kvm_host.h

@@ -35,6 +35,13 @@
 #define KVM_MMIO_SIZE 8
 #endif
 
+/*
+ * The bit 16 ~ bit 31 of kvm_memory_region::flags are internally used
+ * in kvm, other bits are visible for userspace which are defined in
+ * include/linux/kvm_h.
+ */
+#define KVM_MEMSLOT_INVALID	(1UL << 16)
+
 /*
  * If we support unaligned MMIO, at most one fragment will be split into two:
  */