hvm: add HVM_PARAM_VM_GENERATION_ID_ADDR

HVM_PARAM_VM_GENERATION_ID_ADDR is the guest physical address of the
VM Generation ID.  This parameter will be written by hvmloader and read
by the toolstack when updating the gen. ID (e.g., after restoring from a
snapshot).

A HVM parameter is easier for the save/restore code to work with (than
a XenStore key).

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/include/public/hvm/params.h

@@ -148,6 +148,9 @@
 #define HVM_PARAM_IOREQ_SERVER_PFN 32
 #define HVM_PARAM_NR_IOREQ_SERVER_PAGES 33
 
-#define HVM_NR_PARAMS          34
+/* Location of the VM Generation ID in guest physical address space. */
+#define HVM_PARAM_VM_GENERATION_ID_ADDR 34
+
+#define HVM_NR_PARAMS          35
 
 #endif /* __XEN_PUBLIC_HVM_PARAMS_H__ */