io_uring/zcrx: reject REG_NODEV with large rx_buf_size

The copy fallback path doesn't care about the actual niov size and only
uses first PAGE_SIZE bytes, and any additional space will be wasted.
Since ZCRX_REG_NODEV solely relies on the copy path, it doesn't make
sense to support non-standard rx_buf_len. Reject it for now, and
re-enable once improved.

Fixes: c117280 ("io_uring/zcrx: implement device-less mode for zcrx")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://patch.msgid.link/3e7652d9c27f8ac5d2b141e3af47971f2771fb05.1774780198.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/zcrx.c

@@ -449,6 +449,8 @@ static int io_zcrx_create_area(struct io_zcrx_ifq *ifq,
 			return -EINVAL;
 		buf_size_shift = ilog2(reg->rx_buf_len);
 	}
+	if (!ifq->dev && buf_size_shift != PAGE_SHIFT)
+		return -EOPNOTSUPP;
 
 	ret = -ENOMEM;
 	area = kzalloc_obj(*area);
@@ -462,7 +464,7 @@ static int io_zcrx_create_area(struct io_zcrx_ifq *ifq,
 	if (ifq->dev)
 		area->is_mapped = true;
 
-	if (buf_size_shift > io_area_max_shift(&area->mem)) {
+	if (ifq->dev && buf_size_shift > io_area_max_shift(&area->mem)) {
 		ret = -ERANGE;
 		goto err;
 	}