Re: [PATCH 1/3] binder: Use memset_page() in binder_alloc_clear_buf()

[Todd Kjos <tkjos@google.com>]

On Sat, Apr 23, 2022 at 3:24 AM Fabio M. De Francesco
<fmdefrancesco@gmail.com> wrote:
>
> The use of kmap() is being deprecated in favor of kmap_local_page()
> where it is feasible. With kmap_local_page(), the mapping is per
> thread, CPU local and not globally visible.
>
> binder_alloc_clear_buf() is a function where the use of kmap_local_page()
> in place of kmap() is correctly suited because the mapping is local to the
> thread.
>
> Therefore, use kmap_local_page() / kunmap_local() but, instead of open
> coding these two functions and adding a memset() of the virtual address
> of the mapping, prefer memset_page().
>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>

Acked-by: Todd Kjos <tkjos@google.com>

> ---
>  drivers/android/binder_alloc.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 2ac1008a5f39..0b3f2f569053 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -1175,14 +1175,11 @@ static void binder_alloc_clear_buf(struct binder_alloc *alloc,
>                 unsigned long size;
>                 struct page *page;
>                 pgoff_t pgoff;
> -               void *kptr;
>
>                 page = binder_alloc_get_page(alloc, buffer,
>                                              buffer_offset, &pgoff);
>                 size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
> -               kptr = kmap(page) + pgoff;
> -               memset(kptr, 0, size);
> -               kunmap(page);
> +               memset_page(page, pgoff, 0, size);
>                 bytes -= size;
>                 buffer_offset += size;
>         }
> --
> 2.34.1
>