Re: [PATCH v4] mm/huge_memory: preserve PG_has_hwpoisoned if a folio is split to >0 order

[Lance Yang]

On 2025/10/23 11:05, Zi Yan wrote:
> folio split clears PG_has_hwpoisoned, but the flag should be preserved in
> after-split folios containing pages with PG_hwpoisoned flag if the folio is
> split to >0 order folios. Scan all pages in a to-be-split folio to
> determine which after-split folios need the flag.
>
> An alternatives is to change PG_has_hwpoisoned to PG_maybe_hwpoisoned to
> avoid the scan and set it on all after-split folios, but resulting false
> positive has undesirable negative impact. To remove false positive, caller
> of folio_test_has_hwpoisoned() and folio_contain_hwpoisoned_page() needs to
> do the scan. That might be causing a hassle for current and future callers
> and more costly than doing the scan in the split code. More details are
> discussed in [1].
>
> This issue can be exposed via:
> 1. splitting a has_hwpoisoned folio to >0 order from debugfs interface;
> 2. truncating part of a has_hwpoisoned folio in
>     truncate_inode_partial_folio().
>
> And later accesses to a hwpoisoned page could be possible due to the
> missing has_hwpoisoned folio flag. This will lead to MCE errors.
>
> Link: https://lore.kernel.org/all/CAHbLzkoOZm0PXxE9qwtF4gKR=cpRXrSrJ9V9Pm2DJexs985q4g@xxxxxxxxxxxxxx/ [1]
> Fixes: c010d47f107f ("mm: thp: split huge page to any lower order pages")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---

Good spot! LGTM, feel free to add:

Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>