Re: [PATCH 05/19] mm/gup: Detect huge pfnmap entries in gup-fast

David Hildenbrand
2024-08-09T16:23:59Z

On 09.08.24 18:08, Peter Xu wrote:
> Since gup-fast doesn't have the vma reference, teach it to detect such huge
> pfnmaps by checking the special bit for pmd/pud too, just like ptes.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> mm/gup.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index d19884e097fd..a49f67a512ee 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -3038,6 +3038,9 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
> return 0;
>
> + if (pmd_special(orig))
> + return 0;
> +
> if (pmd_devmap(orig)) {
> if (unlikely(flags & FOLL_LONGTERM))
> return 0;
> @@ -3082,6 +3085,9 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
> if (!pud_access_permitted(orig, flags & FOLL_WRITE))
> return 0;
>
> + if (pud_special(orig))
> + return 0;
> +
> if (pud_devmap(orig)) {
> if (unlikely(flags & FOLL_LONGTERM))
> return 0;

In gup_fast_pte_range() we check after checking pte_devmap(). Do we want
to do it in a similar fashion here, or is there a reason to do it
differently?

Acked-by: David Hildenbrand <david@redhat.com>

--
Cheers,

David / dhildenb