linux-kernel - Re: [PATCH] mm/mempool: fix poisoning order>0 pages with HIGHMEM

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Message-ID: <20251114050410.GA26404@lst.de>
Date: Fri, 14 Nov 2025 06:04:10 +0100
From: Christoph Hellwig <hch@....de>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...two.org>,
	David Rientjes <rientjes@...gle.com>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Harry Yoo <harry.yoo@...cle.com>, Jens Axboe <axboe@...nel.dk>,
	linux-block@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	kernel test robot <oliver.sang@...el.com>,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] mm/mempool: fix poisoning order>0 pages with HIGHMEM

On Thu, Nov 13, 2025 at 07:54:35PM +0100, Vlastimil Babka wrote:
> Christoph found out this is due to the poisoning code not dealing
> properly with CONFIG_HIGHMEM because only the first page is mapped but
> then the whole potentially high-order page is accessed.
> 
> This went unnoticed for years probably because nobody has yet used a
> mempool for order>0 pages before the new block code in -next.

I did a quick audit: and bcache, dm-integrity (config dependent) and the
KASAN unit tests create page based mempools with order > 0.  It looks
like none of those ever got much testing on highmem systems.

The fix looks good:

Reviewed-by: Christoph Hellwig <hch@....de>