Xen/x86: also check kernel mapping in set_foreign_p2m_mapping()

We should not set up further state if either mapping failed; paying
attention to just the user mapping's status isn't enough.

Also use GNTST_okay instead of implying its value (zero).

This is part of XSA-361.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: stable@vger.kernel.org
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

arch/x86/xen/p2m.c

@@ -712,7 +712,8 @@ int set_foreign_p2m_mapping(struct gnttab_map_grant_ref *map_ops,
 		unsigned long mfn, pfn;
 
 		/* Do not add to override if the map failed. */
-		if (map_ops[i].status)
+		if (map_ops[i].status != GNTST_okay ||
+		    (kmap_ops && kmap_ops[i].status != GNTST_okay))
 			continue;
 
 		if (map_ops[i].flags & GNTMAP_contains_pte) {