Anyone who wants to do copy to/from user from a kernel thread, needs
use_mm (like what fs/aio has). Move that into mm/, to make reusing and
exporting easier down the line, and make aio use it. Next intended user,
besides aio, will be vhost-net.
Acked-by: Andrea Arcangeli
Signed-off-by: Michael S. Tsirkin
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds