io_uring/rsrc: improve regbuf iov validation

io_uring/rsrc: improve regbuf iov validation

[ Upstream commit 2e02f9efdbc6c73544e315b7eb85e55a59776b6f ]

Deduplicate io_buffer_validate() calls by moving the checks into
io_sqe_buffer_register(). Now we also don't need special handling in
io_buffer_validate() passing through buffer removal requests. I also
was using it as a cleanup before some other changes.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: cd305ee3633a ("io_uring: defer eventfd signaling when queued from a wakeup handler")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>