linux-kernel - Re: [PATCH v4 14/35] kmsan: Do not round up pg_data

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Date: Tue, 18 Jun 2024 16:37:55 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Ilya Leoshkevich <iii@...ux.ibm.com>
Cc: Alexander Gordeev <agordeev@...ux.ibm.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Christoph Lameter <cl@...ux.com>, David Rientjes <rientjes@...gle.com>, Heiko Carstens <hca@...ux.ibm.com>, 
	Joonsoo Kim <iamjoonsoo.kim@....com>, Marco Elver <elver@...gle.com>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Pekka Enberg <penberg@...nel.org>, 
	Steven Rostedt <rostedt@...dmis.org>, Vasily Gorbik <gor@...ux.ibm.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, Hyeonggon Yoo <42.hyeyoo@...il.com>, kasan-dev@...glegroups.com, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-s390@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v4 14/35] kmsan: Do not round up pg_data_t size

On Thu, Jun 13, 2024 at 5:39 PM Ilya Leoshkevich <iii@...ux.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@...ux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@...gle.com>