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 <[email protected]>
Acked-by: Todd Kjos <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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