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

[Christoph Hellwig]

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@xxxxxx>