netdev - [PATCH net-next 07/20] net, ethtool: Disallow mapped real rxqs to be resized

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Message-ID: <20250919213153.103606-8-daniel@iogearbox.net>
Date: Fri, 19 Sep 2025 23:31:40 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: netdev@...r.kernel.org
Cc: bpf@...r.kernel.org,
	kuba@...nel.org,
	davem@...emloft.net,
	razor@...ckwall.org,
	pabeni@...hat.com,
	willemb@...gle.com,
	sdf@...ichev.me,
	john.fastabend@...il.com,
	martin.lau@...nel.org,
	jordan@...fe.io,
	maciej.fijalkowski@...el.com,
	magnus.karlsson@...el.com,
	David Wei <dw@...idwei.uk>
Subject: [PATCH net-next 07/20] net, ethtool: Disallow mapped real rxqs to be resized

Similar to AF_XDP, do not allow queues in a physical netdev to be
resized by ethtool -L when they are peered.

Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Co-developed-by: David Wei <dw@...idwei.uk>
Signed-off-by: David Wei <dw@...idwei.uk>
---
 net/ethtool/channels.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/ethtool/channels.c b/net/ethtool/channels.c
index ca4f80282448..0ede1075e016 100644
--- a/net/ethtool/channels.c
+++ b/net/ethtool/channels.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
+#include <net/netdev_rx_queue.h>
 #include <net/xdp_sock_drv.h>
 
 #include "netlink.h"
@@ -169,14 +170,19 @@ ethnl_set_channels(struct ethnl_req_info *req_info, struct genl_info *info)
 	if (ret)
 		return ret;
 
-	/* Disabling channels, query zero-copy AF_XDP sockets */
+	/* ensure channels are not busy at the moment */
 	from_channel = channels.combined_count +
 		       min(channels.rx_count, channels.tx_count);
-	for (i = from_channel; i < old_total; i++)
+	for (i = from_channel; i < old_total; i++) {
+		if (netdev_rx_queue_peered(dev, i)) {
+			GENL_SET_ERR_MSG(info, "requested channel counts are too low due to existing queue peering");
+			return -EINVAL;
+		}
 		if (xsk_get_pool_from_qid(dev, i)) {
 			GENL_SET_ERR_MSG(info, "requested channel counts are too low for existing zerocopy AF_XDP sockets");
 			return -EINVAL;
 		}
+	}
 
 	ret = dev->ethtool_ops->set_channels(dev, &channels);
 	return ret < 0 ? ret : 1;
-- 
2.43.0