mm: fix overflow in find_zone_movable_pfns_for_nodes()

If the user set "movablecore=xx" to a large number, corepages will
overflow.  Fix the problem.

Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Acked-by: Tang Chen <tangchen@cn.fujitsu.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -5666,6 +5666,7 @@ static void __init find_zone_movable_pfns_for_nodes(void)
 		 */
 		required_movablecore =
 			roundup(required_movablecore, MAX_ORDER_NR_PAGES);
+		required_movablecore = min(totalpages, required_movablecore);
 		corepages = totalpages - required_movablecore;
 
 		required_kernelcore = max(required_kernelcore, corepages);