netdev - [PATCH net-next 2/2] virtio_net: Implement XDP_FLAGS_NO

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Date:   Sat,  9 Jan 2021 13:49:50 +1100
From:   Charlie Somerville <charlie@...rlie.bz>
To:     davem@...emloft.net, kuba@...nel.org, mst@...hat.com,
        jasowang@...hat.com
Cc:     netdev@...r.kernel.org, Charlie Somerville <charlie@...rlie.bz>
Subject: [PATCH net-next 2/2] virtio_net: Implement XDP_FLAGS_NO_TX support

No send queues will be allocated for XDP filters. Attempts to transmit
packets when no XDP send queues exist will fail with EOPNOTSUPP.

Signed-off-by: Charlie Somerville <charlie@...rlie.bz>
---
 drivers/net/virtio_net.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 508408fbe78f..ed08998765e0 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -485,6 +485,10 @@ static struct send_queue *virtnet_xdp_sq(struct virtnet_info *vi)
 {
 	unsigned int qp;
 
+	/* If no queue pairs are allocated for XDP use, return NULL */
+	if (vi->xdp_queue_pairs == 0)
+		return NULL;
+
 	qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
 	return &vi->sq[qp];
 }
@@ -514,6 +518,11 @@ static int virtnet_xdp_xmit(struct net_device *dev,
 
 	sq = virtnet_xdp_sq(vi);
 
+	/* No send queue exists if program was attached with XDP_NO_TX */
+	if (unlikely(!sq)) {
+		return -EOPNOTSUPP;
+	}
+
 	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK)) {
 		ret = -EINVAL;
 		drops = n;
@@ -1464,7 +1473,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 
 	if (xdp_xmit & VIRTIO_XDP_TX) {
 		sq = virtnet_xdp_sq(vi);
-		if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
+		if (sq && virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
 			u64_stats_update_begin(&sq->stats.syncp);
 			sq->stats.kicks++;
 			u64_stats_update_end(&sq->stats.syncp);
@@ -2388,7 +2397,7 @@ static int virtnet_restore_guest_offloads(struct virtnet_info *vi)
 }
 
 static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
-			   struct netlink_ext_ack *extack)
+			   struct netlink_ext_ack *extack, u32 flags)
 {
 	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
 	struct virtnet_info *vi = netdev_priv(dev);
@@ -2418,7 +2427,7 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 	}
 
 	curr_qp = vi->curr_queue_pairs - vi->xdp_queue_pairs;
-	if (prog)
+	if (prog && !(flags & XDP_FLAGS_NO_TX))
 		xdp_qp = nr_cpu_ids;
 
 	/* XDP requires extra queues for XDP_TX */
@@ -2502,7 +2511,7 @@ static int virtnet_xdp(struct net_device *dev, struct netdev_bpf *xdp)
 {
 	switch (xdp->command) {
 	case XDP_SETUP_PROG:
-		return virtnet_xdp_set(dev, xdp->prog, xdp->extack);
+		return virtnet_xdp_set(dev, xdp->prog, xdp->extack, xdp->flags);
 	default:
 		return -EINVAL;
 	}
-- 
2.30.0