2022-04-23 14:41:57

by Fabio M. De Francesco

Subject: [PATCH 2/3] binder: Use kmap_local_page() in binder_alloc_copy_user_to_buffer()

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_copy_user_to_buffer() 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().

Signed-off-by: Fabio M. De Francesco <[email protected]>
---
drivers/android/binder_alloc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 0b3f2f569053..0875c463c002 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -1217,9 +1217,9 @@ binder_alloc_copy_user_to_buffer(struct binder_alloc *alloc,
page = binder_alloc_get_page(alloc, buffer,
buffer_offset, &pgoff);
size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
- kptr = kmap(page) + pgoff;
+ kptr = kmap_local_page(page) + pgoff;
ret = copy_from_user(kptr, from, size);
- kunmap(page);
+ kunmap_local(kptr);
if (ret)
return bytes - size + ret;
bytes -= size;
--
2.34.1

2022-04-24 07:36:36

by Todd Kjos

Subject: Re: [PATCH 2/3] binder: Use kmap_local_page() in binder_alloc_copy_user_to_buffer()

On Sat, Apr 23, 2022 at 3:24 AM Fabio M. De Francesco
<[email protected]> 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_copy_user_to_buffer() 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().
>
> Signed-off-by: Fabio M. De Francesco <[email protected]>

Acked-by: Todd Kjos <[email protected]>

> ---
> drivers/android/binder_alloc.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 0b3f2f569053..0875c463c002 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -1217,9 +1217,9 @@ binder_alloc_copy_user_to_buffer(struct binder_alloc *alloc,
> page = binder_alloc_get_page(alloc, buffer,
> buffer_offset, &pgoff);
> size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
> - kptr = kmap(page) + pgoff;
> + kptr = kmap_local_page(page) + pgoff;
> ret = copy_from_user(kptr, from, size);
> - kunmap(page);
> + kunmap_local(kptr);
> if (ret)
> return bytes - size + ret;
> bytes -= size;
> --
> 2.34.1
>