x86/xen: Do not clip xen_e820_map to xen_e820_map_entries when sanitizing map

commit 64c98e7f upstream.

Sanitizing the e820 map may produce extra E820 entries which would result in
the topmost E820 entries being removed. The removed entries would typically
include the top E820 usable RAM region and thus result in the domain having
signicantly less RAM available to it.

Fix by allowing sanitize_e820_map to use the full size of the allocated E820
array.
Signed-off-by: Malcolm Crossley <malcolm.crossley@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
[ luis: backported to 3.16:
  - use 'map' instead of 'xen_e820_map_entries' ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

arch/x86/xen/setup.c

@@ -385,7 +385,7 @@ char * __init xen_memory_setup(void)
 		xen_ignore_unusable(map, memmap.nr_entries);
 
 	/* Make sure the Xen-supplied memory map is well-ordered. */
-	sanitize_e820_map(map, memmap.nr_entries, &memmap.nr_entries);
+	sanitize_e820_map(map, ARRAY_SIZE(map), &memmap.nr_entries);
 
 	max_pages = xen_get_max_pages();
 	if (max_pages > max_pfn)