Re: [PATCH v2] tee: shm: fix slab page refcounting

[Jens Wiklander]

Hi Marco,

On Tue, Mar 25, 2025 at 9:07 PM Marco Felsch <m.felsch@xxxxxxxxxxxxxx> wrote:
>
> Skip manipulating the refcount in case of slab pages according commit
> b9c0e49abfca ("mm: decline to manipulate the refcount on a slab page").
>
> Fixes: b9c0e49abfca ("mm: decline to manipulate the refcount on a slab page")
> Signed-off-by: Marco Felsch <m.felsch@xxxxxxxxxxxxxx>
> ---
> v2:
> - Make use of page variable
> v1:
> - https://lore.kernel.org/all/20250325195021.3589797-1-m.felsch@xxxxxxxxxxxxxx/
>
>  drivers/tee/tee_shm.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
> index daf6e5cfd59a..35f0ac359b12 100644
> --- a/drivers/tee/tee_shm.c
> +++ b/drivers/tee/tee_shm.c
> @@ -19,16 +19,24 @@ static void shm_put_kernel_pages(struct page **pages, size_t page_count)
>  {
>         size_t n;
>
> -       for (n = 0; n < page_count; n++)
> -               put_page(pages[n]);
> +       for (n = 0; n < page_count; n++) {
> +               struct page *page = pages[n];
> +
> +               if (!PageSlab(page))
> +                       put_page(page);
> +       }
>  }
>
>  static void shm_get_kernel_pages(struct page **pages, size_t page_count)
>  {
>         size_t n;
>
> -       for (n = 0; n < page_count; n++)
> -               get_page(pages[n]);
> +       for (n = 0; n < page_count; n++) {
> +               struct page *page = pages[n];
> +
> +               if (!PageSlab(page))
> +                       get_page(page);

b9c0e49abfca ("mm: decline to manipulate the refcount on a slab page")
mentions that more page types will have a zero refcount in the longer
term. So we'll need to add exception after exception here. Is there a
helper function somewhere to get all the pages we need? Or can we do
this differently?

Cheers,
Jens

> +       }
>  }
>
>  static void release_registered_pages(struct tee_shm *shm)
> --
> 2.39.5
>