Re: [PATCH v2 2/3] mm/hugetlb: Preserve persistent flags when returning folios to the pool

[Qi Zheng]

On 11/2/26 10:49 AM, Kaitao Cheng wrote:
> From: Kaitao Cheng <chengkaitao@xxxxxxxxxx>
>
> add_hugetlb_folio() returns a folio to the HugeTLB pool when vmemmap
> restoration fails. It clears folio->private and restores only
> HPG_vmemmap_optimized, losing other flags that must survive the rollback.
>
> Clearing HPG_cma causes a later free to bypass the CMA release path,
> leaving the CMA allocation bitmap set. Clearing HPG_raw_hwp_unreliable
> loses the indication that the locations of poisoned subpages are unknown,
> undermining the checks that prevent freeing or unpoisoning such folios.
>
> Preserve the existing flags instead of resetting folio->private. Callers
> already clear HPG_restore_reserve, HPG_migratable and HPG_freed before
> returning a folio to the pool. Clear HPG_temporary in free_huge_folio()
> before attempting to free a temporary folio, so a failed vmemmap restore
> does not leave that flag set on a folio returned as surplus.
>
> Add a VM_WARN_ON_ONCE_FOLIO() check for flags other than
> HPG_vmemmap_optimized, HPG_raw_hwp_unreliable and HPG_cma to detect
> incomplete transient flag cleanup.
>
> Fixes: 161df60e9e89 ("mm, hwpoison, hugetlb: support saving mechanism of raw error pages")
> Fixes: d2d786714080 ("mm/hugetlb: enable bootmem allocation from CMA areas")
> Closes: https://sashiko.dev/#/bug/linux-5363eb09-9c3c-4f8b-9f3c-a998a8c4b258
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Suggested-by: Muchun Song <muchun.song@xxxxxxxxx>
> Suggested-by: Zi Yan <ziy@xxxxxxxxxx>
> Signed-off-by: Kaitao Cheng <chengkaitao@xxxxxxxxxx>
> ---
>   mm/hugetlb.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)

Acked-by: Qi Zheng <qi.zheng@xxxxxxxxx>

Thanks,
Qi