Re: [PATCH v4 02/19] mm/hugetlb_vmemmap: Fix __hugetlb_vmemmap_optimize_folios()

[Frank van der Linden]

On Thu, Jun 11, 2026 at 8:59 PM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
>
> __hugetlb_vmemmap_optimize_folios() uses incorrect arguments when handling
> bootmem HugeTLB folios.
>
> The section number passed to register_page_bootmem_memmap() is derived from
> the vmemmap virtual address of folio->page instead of the folio PFN, so the
> bootmem memmap metadata can be registered against the wrong section. The
> helper is also given HUGETLB_VMEMMAP_RESERVE_SIZE even though it expects a
> page count, not a size in bytes. In addition, the write-protect range is
> based on pages_per_huge_page(h), which does not cover the full HugeTLB
> vmemmap area and can leave part of the shared tail vmemmap mapping writable.
>
> Fix the section lookup to use folio_pfn(folio), use
> HUGETLB_VMEMMAP_RESERVE_PAGES when registering the reserved memmap pages, and
> use hugetlb_vmemmap_size(h) for the write-protect range.
>
> Fixes: 752fe17af693 ("mm/hugetlb: add pre-HVO framework")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> Acked-by: Oscar Salvador <osalvador@xxxxxxx>
> ---
>  mm/hugetlb_vmemmap.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index c713c0d2593a..ea6af85bfec1 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -635,12 +635,12 @@ static void __hugetlb_vmemmap_optimize_folios(struct hstate *h,
>                          * mirrored tail page structs RO.
>                          */
>                         spfn = (unsigned long)&folio->page;
> -                       epfn = spfn + pages_per_huge_page(h);
> +                       epfn = spfn + hugetlb_vmemmap_size(h);
>                         vmemmap_wrprotect_hvo(spfn, epfn, folio_nid(folio),
>                                         HUGETLB_VMEMMAP_RESERVE_SIZE);
> -                       register_page_bootmem_memmap(pfn_to_section_nr(spfn),
> +                       register_page_bootmem_memmap(pfn_to_section_nr(folio_pfn(folio)),
>                                         &folio->page,
> -                                       HUGETLB_VMEMMAP_RESERVE_SIZE);
> +                                       HUGETLB_VMEMMAP_RESERVE_PAGES);
>                         continue;
>                 }
>

Thanks for fixing my mistakes!

Reviewed-by: Frank van der Linden <fvdl@xxxxxxxxxx>