netdev - [PATCH net-next] net/mlx5e: Modify mlx5e_xdp

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Message-ID: <e25c6c0c-1e2a-48c2-9606-5f51f36afbf0@bytedance.com>
Date: Thu, 30 Oct 2025 17:42:50 -0700
From: Zijian Zhang <zijianzhang@...edance.com>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
 edumazet@...gle.com, andrew+netdev@...n.ch, saeedm@...dia.com,
 gal@...dia.com, leonro@...dia.com, witu@...dia.com, parav@...dia.com,
 tariqt@...dia.com
Subject: [PATCH net-next] net/mlx5e: Modify mlx5e_xdp_xmit sq selection

From: Zijian Zhang <zijianzhang@...edance.com>

When performing XDP_REDIRECT from one mlnx device to another, using
smp_processor_id() to select the queue may go out-of-range.

Assume eth0 is redirecting a packet to eth1, eth1 is configured
with only 8 channels, while eth0 has its RX queues pinned to
higher-numbered CPUs (e.g. CPU 12). When a packet is received on
such a CPU and redirected to eth1, the driver uses smp_processor_id()
as the SQ index. Since the CPU ID is larger than the number of queues
on eth1, the lookup (priv->channels.c[sq_num]) goes out of range and
the redirect fails.

This patch fixes the issue by mapping the CPU ID to a valid channel
index using modulo arithmetic:

     sq_num = smp_processor_id() % priv->channels.num;

With this change, XDP_REDIRECT works correctly even when the source
device uses high CPU affinities and the target device has fewer TX
queues.

Signed-off-by: Zijian Zhang <zijianzhang@...edance.com>
---
  drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c | 6 +-----
  1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c 
b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
index 5d51600935a6..61394257c65f 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
@@ -855,11 +855,7 @@ int mlx5e_xdp_xmit(struct net_device *dev, int n, 
struct xdp_frame **frames,
  	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK))
  		return -EINVAL;

-	sq_num = smp_processor_id();
-
-	if (unlikely(sq_num >= priv->channels.num))
-		return -ENXIO;
-
+	sq_num = smp_processor_id() % priv->channels.num;
  	sq = priv->channels.c[sq_num]->xdpsq;

  	for (i = 0; i < n; i++) {
-- 
2.20.1