Re: [PATCH AUTOSEL 5.4 10/13] kmsan: disable physical page merging in biovec

[Eric Biggers]

On Mon, Oct 17, 2022 at 08:10:59PM -0400, Sasha Levin wrote:
> From: Alexander Potapenko <glider@xxxxxxxxxx>
> 
> [ Upstream commit f630a5d0ca59a6e73b61e3f82c371dc230da99ff ]
> 
> KMSAN metadata for adjacent physical pages may not be adjacent, therefore
> accessing such pages together may lead to metadata corruption.  We disable
> merging pages in biovec to prevent such corruptions.
> 
> Link: https://lkml.kernel.org/r/20220915150417.722975-28-glider@xxxxxxxxxx
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
> Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> Cc: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Petr Mladek <pmladek@xxxxxxxx>
> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
> Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  block/blk.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/block/blk.h b/block/blk.h
> index ee3d5664d962..3358ef4244fe 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -79,6 +79,13 @@ static inline bool biovec_phys_mergeable(struct request_queue *q,
>  	phys_addr_t addr1 = page_to_phys(vec1->bv_page) + vec1->bv_offset;
>  	phys_addr_t addr2 = page_to_phys(vec2->bv_page) + vec2->bv_offset;
>  
> +	/*
> +	 * Merging adjacent physical pages may not work correctly under KMSAN
> +	 * if their metadata pages aren't adjacent. Just disable merging.
> +	 */
> +	if (IS_ENABLED(CONFIG_KMSAN))
> +		return false;
> +
>  	if (addr1 + vec1->bv_len != addr2)
>  		return false;
>  	if (xen_domain() && !xen_biovec_phys_mergeable(vec1, vec2->bv_page))

So KMSAN is being backported to 5.4?

- Eric