[PATCH net-next 2/3] veth: link RX queues to their NAPI instances

[Tianyi Gao <tianyi@cloudflare.com>]

veth does not link its RX queues to their NAPI instances. queue-get
therefore reports no napi-id for them. napi-get lists the NAPI instances
of a veth, and their thread PIDs when NAPI is threaded. It does not show
which RX queue each instance polls. Userspace cannot tell which NAPI
thread to pin for a given queue, or which NAPI to change with napi-set.

There is also no way to busy poll an AF_XDP socket bound to a veth
queue. Since commit b95ed5517354 ("xsk: Bring back busy polling support
in XDP_COPY"), xsk_bind() takes the NAPI ID of a copy-mode socket from
rxq->napi. veth never sets rxq->napi, so the socket gets no NAPI ID.

Call netif_queue_set_napi() after napi_enable(), which assigns the NAPI
ID. Call it again with NULL before napi_disable(). veth is not ops
locked, so netif_queue_set_napi() requires RTNL. veth enables and
disables NAPI only in ndo_open, ndo_stop, ndo_bpf, ndo_set_features and
ethtool's set_channels. All of them are called under RTNL.

Suggested-by: Jesper Dangaard Brouer <hawk@kernel.org>
Signed-off-by: Tianyi Gao <tianyi@cloudflare.com>
---
 drivers/net/veth.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index a3570547ee99..c00ebc5b96c7 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1062,6 +1062,8 @@ static int veth_napi_enable_range(struct net_device *dev, int start, int end)
 		netif_napi_add(dev, &rq->xdp_napi, veth_poll);
 		rcu_assign_pointer(rq->xdp_prog, priv->_xdp_prog);
 		napi_enable(&rq->xdp_napi);
+		netif_queue_set_napi(dev, i, NETDEV_QUEUE_TYPE_RX,
+				     &rq->xdp_napi);
 		rcu_assign_pointer(priv->rq[i].napi, &priv->rq[i].xdp_napi);
 	}
 
@@ -1094,6 +1096,7 @@ static void veth_napi_del_range(struct net_device *dev, int start, int end)
 		struct veth_rq *rq = &priv->rq[i];
 
 		rcu_assign_pointer(priv->rq[i].napi, NULL);
+		netif_queue_set_napi(dev, i, NETDEV_QUEUE_TYPE_RX, NULL);
 		napi_disable(&rq->xdp_napi);
 		rcu_assign_pointer(rq->xdp_prog, NULL);
 		__netif_napi_del(&rq->xdp_napi);
-- 
2.56.0