diff mbox series

[v4,14/35] kmsan: Do not round up pg_data_t size

Message ID 20240613153924.961511-15-iii@linux.ibm.com (mailing list archive)
State Superseded
Headers show
Series kmsan: Enable on s390 | expand

Commit Message

Ilya Leoshkevich June 13, 2024, 3:34 p.m. UTC 
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.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 mm/kmsan/init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Alexander Potapenko June 18, 2024, 2:37 p.m. UTC | #1 
On Thu, Jun 13, 2024 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote:
>
> 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.

Nice catch, thanks!

> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
diff mbox series

Patch

diff --git a/mm/kmsan/init.c b/mm/kmsan/init.c
index 3ac3b8921d36..9de76ac7062c 100644
--- a/mm/kmsan/init.c
+++ b/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;