linux-kernel - Re: [PATCH 1/3] binder: Use memset_page() in binder_alloc_clear

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Message-ID: <CAHRSSEwQSB=9rcCG+LmFUgrRHdsLDkstOW0qy-5Uw2xEm0SniA@mail.gmail.com>
Date:   Sat, 23 Apr 2022 08:43:00 -0700
From:   Todd Kjos <tkjos@...gle.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <brauner@...nel.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Ira Weiny <ira.weiny@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] binder: Use memset_page() in binder_alloc_clear_buf()

On Sat, Apr 23, 2022 at 3:24 AM Fabio M. De Francesco
<fmdefrancesco@...il.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@...il.com>

Acked-by: Todd Kjos <tkjos@...gle.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
>