binder: Use memcpy_{to,from}_page() in binder_alloc_do_buffer_copy()

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 <christophe.jaillet@wanadoo.fr>
Acked-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Link: https://lore.kernel.org/r/20220425175754.8180-4-fmdefrancesco@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 0875c463c002ac66eb31a37ec6f6a5b92a0a4c98..5649a0371a1f2c8b553957f613b4d271d21919ee 100644 (file)
--- 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;