Re: [PATCH v1 1/4] mm/hugetlb: fix hugetlb_pmd_shared()

[Lance Yang]

On 2025/12/6 13:55, Lance Yang wrote:
> From: Lance Yang <lance.yang@xxxxxxxxx>
>
>
> On Fri,  5 Dec 2025 22:35:55 +0100, David Hildenbrand (Red Hat) wrote:
> > We switched from (wrongly) using the page count to an independent
> > shared count. Now, shared page tables have a refcount of 1 (excluding
> > speculative references) and instead use ptdesc->pt_share_count to
> > identify sharing.
> >
> > We didn't convert hugetlb_pmd_shared(), so right now, we would never
> > detect a shared PMD table as such, because sharing/unsharing no longer
> > touches the refcount of a PMD table.
> >
> > Page migration, like mbind() or migrate_pages() would allow for migrating
> > folios mapped into such shared PMD tables, even though the folios are
> > not exclusive. In smaps we would account them as "private" although they
> > are "shared", and we would be wrongly setting the PM_MMAP_EXCLUSIVE in the
> > pagemap interface.
> >
> > Fix it by properly using ptdesc_pmd_is_shared() in hugetlb_pmd_shared().
> >
> > Fixes: 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count")
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Cc: Liu Shixin <liushixin2@xxxxxxxxxx>
> > Signed-off-by: David Hildenbrand (Red Hat) <david@xxxxxxxxxx>
> > ---
>
> Good catch! Feel free to add:
>
> Reviewed-by: Lance yang <lance.yang@xxxxxxxxx>

Actually:

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