s390/kasan: add kdump support

If kasan enabled kernel is used as crash kernel it crashes itself with
program check loop during kdump execution. The reason for that is that
kasan shadow memory backed by pages beyond OLDMEM_SIZE. Make kasan memory
allocator respect physical memory limit imposed by kdump.
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/mm/kasan_init.c

@@ -261,6 +261,8 @@ void __init kasan_early_init(void)
 	/* respect mem= cmdline parameter */
 	if (memory_end_set && memsize > memory_end)
 		memsize = memory_end;
+	if (IS_ENABLED(CONFIG_CRASH_DUMP) && OLDMEM_BASE)
+		memsize = min(memsize, OLDMEM_SIZE);
 	memsize = min(memsize, KASAN_SHADOW_START);
 
 	if (IS_ENABLED(CONFIG_KASAN_S390_4_LEVEL_PAGING)) {