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Date: Fri, 14 Nov 2025 06:04:10 +0100
From: Christoph Hellwig <hch@lst.de>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@gentwo.org>,
	David Rientjes <rientjes@google.com>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Harry Yoo <harry.yoo@oracle.com>, Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org,
	kernel test robot <oliver.sang@intel.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] mm/mempool: fix poisoning order>0 pages with HIGHMEM
Message-ID: <20251114050410.GA26404@lst.de>
References: <20251113-mempool-poison-v1-1-233b3ef984c3@suse.cz>
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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@lst.de>