kmsan: do not round up pg_data_t size

x86's alloc_node_data() rounds up node data size to PAGE_SIZE.  It's not
explained why it's needed, but it's most likely for performance reasons,
since the padding bytes are not used anywhere.  Some other architectures
do it as well, e.g., mips rounds it up to the cache line size.

kmsan_init_shadow() initializes metadata for each node data and assumes
the x86 rounding, which does not match other architectures.  This may
cause the range end to overshoot the end of available memory, in turn
causing virt_to_page_or_null() in kmsan_init_alloc_meta_for_range() to
return NULL, which leads to kernel panic shortly after.

Since the padding bytes are not used, drop the rounding.

Link: https://lkml.kernel.org/r/20240621113706.315500-16-iii@linux.ibm.com
Signed-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/init.c

@@ -72,7 +72,7 @@ static void __init kmsan_record_future_shadow_range(void *start, void *end)
  */
 void __init kmsan_init_shadow(void)
 {
-	const size_t nd_size = roundup(sizeof(pg_data_t), PAGE_SIZE);
+	const size_t nd_size = sizeof(pg_data_t);
 	phys_addr_t p_start, p_end;
 	u64 loop;
 	int nid;