kmsan: use ALIGN_DOWN() in kmsan_get_metadata()

Improve the readability by replacing the custom aligning logic with
ALIGN_DOWN().  Unlike other places where a similar sequence is used, there
is no size parameter that needs to be adjusted, so the standard macro
fits.

Link: https://lkml.kernel.org/r/20240621113706.315500-15-iii@linux.ibm.comSigned-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <kasan-dev@googlegroups.com>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/kmsan/shadow.c

@@ -123,14 +123,12 @@ struct shadow_origin_ptr kmsan_get_shadow_origin_ptr(void *address, u64 size,
  */
 void *kmsan_get_metadata(void *address, bool is_origin)
 {
-	u64 addr = (u64)address, pad, off;
+	u64 addr = (u64)address, off;
 	struct page *page;
 	void *ret;
 
-	if (is_origin && !IS_ALIGNED(addr, KMSAN_ORIGIN_SIZE)) {
-		pad = addr % KMSAN_ORIGIN_SIZE;
-		addr -= pad;
-	}
+	if (is_origin)
+		addr = ALIGN_DOWN(addr, KMSAN_ORIGIN_SIZE);
 	address = (void *)addr;
 	if (kmsan_internal_is_vmalloc_addr(address) ||
 	    kmsan_internal_is_module_addr(address))