hvm save/restore: Use a GUEST_HANDLE_64 rather than an ordinary GUEST_HANDLE

when getting the HVM context so as 32 bit dom0s on a 64 bit hypervisor
do the right thing.

Signed-off-by: Steven Smith <sos22@cam.ac.uk>

xen/include/public/domctl.h

@@ -394,8 +394,10 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_settimeoffset_t);
 #define XEN_DOMCTL_sethvmcontext     34
 typedef struct xen_domctl_hvmcontext {
     uint32_t size; /* IN/OUT: size of buffer / bytes filled */
-    XEN_GUEST_HANDLE(uint8_t) buffer; /* IN/OUT: data, or call gethvmcontext 
-                                       * with NULL buffer to get size req'd */
+    XEN_GUEST_HANDLE_64(uint8_t) buffer; /* IN/OUT: data, or call
+                                          * gethvmcontext with NULL
+                                          * buffer to get size
+                                          * req'd */
 } xen_domctl_hvmcontext_t;
 DEFINE_XEN_GUEST_HANDLE(xen_domctl_hvmcontext_t);