[PATCH net-next v6 3/4] virtio-net: Map NAPIs to queues

[Joe Damato <jdamato@fastly.com>]

Use netif_queue_set_napi to map NAPIs to queue IDs so that the mapping
can be accessed by user apps. Note that the netif_queue_set_napi
currently requires RTNL, so care must be taken to ensure RTNL is held on
paths where this API might be reached.

The paths in the driver where this API can be reached appear to be:

  - ndo_open, ndo_close, which hold RTNL so no driver change is needed.
  - rx_pause, rx_resume, tx_pause, tx_resume are reached either via
    an ethtool ioctl or via XSK - neither path requires a driver change.
  - power management paths (which call open and close), which have been
    updated to hold/release RTNL.

$ ethtool -i ens4 | grep driver
driver: virtio_net

$ sudo ethtool -L ens4 combined 4

$ ./tools/net/ynl/pyynl/cli.py \
       --spec Documentation/netlink/specs/netdev.yaml \
       --dump queue-get --json='{"ifindex": 2}'
[{'id': 0, 'ifindex': 2, 'napi-id': 8289, 'type': 'rx'},
 {'id': 1, 'ifindex': 2, 'napi-id': 8290, 'type': 'rx'},
 {'id': 2, 'ifindex': 2, 'napi-id': 8291, 'type': 'rx'},
 {'id': 3, 'ifindex': 2, 'napi-id': 8292, 'type': 'rx'},
 {'id': 0, 'ifindex': 2, 'type': 'tx'},
 {'id': 1, 'ifindex': 2, 'type': 'tx'},
 {'id': 2, 'ifindex': 2, 'type': 'tx'},
 {'id': 3, 'ifindex': 2, 'type': 'tx'}]

Note that virtio_net has TX-only NAPIs which do not have NAPI IDs, so
the lack of 'napi-id' in the above output is expected.

Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 drivers/net/virtio_net.c | 40 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 36 insertions(+), 4 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index e578885c1093..7bd63a677123 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2823,13 +2823,18 @@ static void virtnet_napi_do_enable(struct virtqueue *vq,
 
 static void virtnet_napi_enable(struct receive_queue *rq)
 {
+	struct virtnet_info *vi = rq->vq->vdev->priv;
+	int qidx = vq2rxq(rq->vq);
+
 	virtnet_napi_do_enable(rq->vq, &rq->napi);
+	netif_queue_set_napi(vi->dev, qidx, NETDEV_QUEUE_TYPE_RX, &rq->napi);
 }
 
 static void virtnet_napi_tx_enable(struct send_queue *sq)
 {
 	struct virtnet_info *vi = sq->vq->vdev->priv;
 	struct napi_struct *napi = &sq->napi;
+	int qidx = vq2txq(sq->vq);
 
 	if (!napi->weight)
 		return;
@@ -2843,20 +2848,28 @@ static void virtnet_napi_tx_enable(struct send_queue *sq)
 	}
 
 	virtnet_napi_do_enable(sq->vq, napi);
+	netif_queue_set_napi(vi->dev, qidx, NETDEV_QUEUE_TYPE_TX, napi);
 }
 
 static void virtnet_napi_tx_disable(struct send_queue *sq)
 {
+	struct virtnet_info *vi = sq->vq->vdev->priv;
 	struct napi_struct *napi = &sq->napi;
+	int qidx = vq2txq(sq->vq);
 
-	if (napi->weight)
+	if (napi->weight) {
+		netif_queue_set_napi(vi->dev, qidx, NETDEV_QUEUE_TYPE_TX, NULL);
 		napi_disable(napi);
+	}
 }
 
 static void virtnet_napi_disable(struct receive_queue *rq)
 {
+	struct virtnet_info *vi = rq->vq->vdev->priv;
 	struct napi_struct *napi = &rq->napi;
+	int qidx = vq2rxq(rq->vq);
 
+	netif_queue_set_napi(vi->dev, qidx, NETDEV_QUEUE_TYPE_RX, NULL);
 	napi_disable(napi);
 }
 
@@ -2870,9 +2883,23 @@ static void refill_work(struct work_struct *work)
 	for (i = 0; i < vi->curr_queue_pairs; i++) {
 		struct receive_queue *rq = &vi->rq[i];
 
-		virtnet_napi_disable(rq);
+		/*
+		 * When queue API support is added in the future and the call
+		 * below becomes napi_disable_locked, this driver will need to
+		 * be refactored.
+		 *
+		 * One possible solution would be to:
+		 *   - cancel refill_work with cancel_delayed_work (note:
+		 *     non-sync)
+		 *   - cancel refill_work with cancel_delayed_work_sync in
+		 *     virtnet_remove after the netdev is unregistered
+		 *   - wrap all of the work in a lock (perhaps the netdev
+		 *     instance lock)
+		 *   - check netif_running() and return early to avoid a race
+		 */
+		napi_disable(&rq->napi);
 		still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
-		virtnet_napi_enable(rq);
+		virtnet_napi_do_enable(rq->vq, &rq->napi);
 
 		/* In theory, this can happen: if we don't get any buffers in
 		 * we will *never* try to fill again.
@@ -5650,8 +5677,11 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
 	netif_tx_lock_bh(vi->dev);
 	netif_device_detach(vi->dev);
 	netif_tx_unlock_bh(vi->dev);
-	if (netif_running(vi->dev))
+	if (netif_running(vi->dev)) {
+		rtnl_lock();
 		virtnet_close(vi->dev);
+		rtnl_unlock();
+	}
 }
 
 static int init_vqs(struct virtnet_info *vi);
@@ -5671,7 +5701,9 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 	enable_rx_mode_work(vi);
 
 	if (netif_running(vi->dev)) {
+		rtnl_lock();
 		err = virtnet_open(vi->dev);
+		rtnl_unlock();
 		if (err)
 			return err;
 	}
-- 
2.45.2