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

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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>
This commit is contained in:
Fabio M. De Francesco 2022-04-25 19:57:54 +02:00 committed by Greg Kroah-Hartman
parent 1d625960e4
commit e88a6a8fec
1 changed files with 2 additions and 11 deletions
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13
drivers/android/binder_alloc.c
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@ -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;