Use kmap_local_page() in binder_alloc.c because kmap() and kmap_atomic()
are being deprecated and kmap_local_page() is preferred where it is
feasible.
With kmap_local_page(), the mapping is per thread, CPU local and not
globally visible. Furthermore, the mapping can be acquired from any
context, including interrupts.
Fabio M. De Francesco (3):
binder: Use memset_page() in binder_alloc_clear_buf()
binder: Use kmap_local_page() in binder_alloc_copy_user_to_buffer()
binder: Use memcpy_{to,from}_page() in binder_alloc_do_buffer_copy()
drivers/android/binder_alloc.c | 22 +++++-----------------
1 file changed, 5 insertions(+), 17 deletions(-)
--
2.34.1
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().
Cc: Christophe JAILLET <[email protected]>
Acked-by: Todd Kjos <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
---
v1->v2: Add Todd Kjos's tag in the commit message (thanks!).
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
The use of kmap_atomic() is being deprecated in favor of kmap_local_page()
where it is feasible. Each call of kmap_atomic() in the kernel creates
a non-preemptible section and disable pagefaults. This could be a source
of unwanted latency, so kmap_local_page() should be preferred.
With kmap_local_page(), the mapping is per thread, CPU local and not
globally visible. Furthermore, the mapping can be acquired from any context
(including interrupts). binder_alloc_do_buffer_copy() is a function where
the use of kmap_local_page() in place of kmap_atomic() is correctly suited.
Use kmap_local_page() / kunmap_local() in place of kmap_atomic() /
kunmap_atomic() but, instead of open coding the mappings and call memcpy()
to and from the virtual addresses of the mapped pages, prefer the use of
the memcpy_{to,from}_page() wrappers (as suggested by Christophe
Jaillet).
Cc: Christophe JAILLET <[email protected]>
Acked-by: Todd Kjos <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
---
v1->v2: Add Todd Kjos's tag in the commit message (thanks!); re-write
the subject which referred to another function (my fault!); use the
memcpy_{to,from}_page() (as suggested by Christophe - thanks!); extend
and rework the commit message to say something about the use of the
above-mentioned wrappers.
drivers/android/binder_alloc.c | 13 ++-----------
1 file changed, 2 insertions(+), 11 deletions(-)
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 0875c463c002..5649a0371a1f 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -1244,23 +1244,14 @@ static int binder_alloc_do_buffer_copy(struct binder_alloc *alloc,
unsigned long size;
struct page *page;
pgoff_t pgoff;
- void *tmpptr;
- void *base_ptr;
page = binder_alloc_get_page(alloc, buffer,
buffer_offset, &pgoff);
size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
- base_ptr = kmap_atomic(page);
- tmpptr = base_ptr + pgoff;
if (to_buffer)
- memcpy(tmpptr, ptr, size);
+ memcpy_to_page(page, pgoff, ptr, size);
else
- memcpy(ptr, tmpptr, size);
- /*
- * kunmap_atomic() takes care of flushing the cache
- * if this device has VIVT cache arch
- */
- kunmap_atomic(base_ptr);
+ memcpy_from_page(ptr, page, pgoff, size);
bytes -= size;
pgoff = 0;
ptr = ptr + size;
--
2.34.1
On Mon, Apr 25, 2022 at 07:57:51PM +0200, Fabio M. De Francesco wrote:
> Use kmap_local_page() in binder_alloc.c because kmap() and kmap_atomic()
> are being deprecated and kmap_local_page() is preferred where it is
> feasible.
>
> With kmap_local_page(), the mapping is per thread, CPU local and not
> globally visible. Furthermore, the mapping can be acquired from any
> context, including interrupts.
For the series:
Reviewed-by: Ira Weiny <[email protected]>
>
> Fabio M. De Francesco (3):
> binder: Use memset_page() in binder_alloc_clear_buf()
> binder: Use kmap_local_page() in binder_alloc_copy_user_to_buffer()
> binder: Use memcpy_{to,from}_page() in binder_alloc_do_buffer_copy()
>
> drivers/android/binder_alloc.c | 22 +++++-----------------
> 1 file changed, 5 insertions(+), 17 deletions(-)
>
> --
> 2.34.1
>