io_uring: increase max number of reg buffers

Since recent changes instead of storing a large array of struct
io_mapped_ubuf, we store pointers to them, that is 4 times slimmer and
we should not to so worry about restricting max number of registererd
buffer slots, increase the limit 4 times.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d3dee1da37f46da416aa96a16bf9e5094e10584d.1620990371.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -100,6 +100,8 @@
 #define IORING_MAX_RESTRICTIONS	(IORING_RESTRICTION_LAST + \
 				 IORING_REGISTER_LAST + IORING_OP_LAST)
 
+#define IORING_MAX_REG_BUFFERS	(1U << 14)
+
 #define SQE_VALID_FLAGS	(IOSQE_FIXED_FILE|IOSQE_IO_DRAIN|IOSQE_IO_LINK|	\
 				IOSQE_IO_HARDLINK | IOSQE_ASYNC | \
 				IOSQE_BUFFER_SELECT)
@@ -8389,7 +8391,7 @@ static int io_sqe_buffers_register(struct io_ring_ctx *ctx, void __user *arg,
 
 	if (ctx->user_bufs)
 		return -EBUSY;
-	if (!nr_args || nr_args > UIO_MAXIOV)
+	if (!nr_args || nr_args > IORING_MAX_REG_BUFFERS)
 		return -EINVAL;
 	ret = io_rsrc_node_switch_start(ctx);
 	if (ret)