virtio-net: send gratuitous packets when needed

As hypervior does not have the knowledge of guest network configuration, it's
better to ask guest to send gratuitous packets when needed.

This patch implements VIRTIO_NET_F_GUEST_ANNOUNCE feature: hypervisor would
notice the guest when it thinks it's time for guest to announce the link
presnece. Guest tests VIRTIO_NET_S_ANNOUNCE bit during config change interrupt
and woule send gratuitous packets through netif_notify_peers() and ack the
notification through ctrl vq.

We need to make sure the atomicy of read and ack in guest otherwise we may ack
more times than being notified. This is done through handling the whole config
change interrupt in an non-reentrant workqueue.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 59 insertions, 5 deletions

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index af8acc85f4bb..fa58c7869954 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -66,12 +66,21 @@ struct virtnet_info {
         /* Host will merge rx buffers for big packets (shake it! shake it!) */
         bool mergeable_rx_bufs;
 
+        /* enable config space updates */
+        bool config_enable;
+
         /* Active statistics */
         struct virtnet_stats __percpu *stats;
 
         /* Work struct for refilling if we run low on memory. */
         struct delayed_work refill;
 
+        /* Work struct for config space updates */
+        struct work_struct config_work;
+
+        /* Lock for config space updates */
+        struct mutex config_lock;
+
         /* Chain pages by the private ptr. */
         struct page *pages;
 
@@ -780,6 +789,16 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
         return status == VIRTIO_NET_OK;
 }
 
+static void virtnet_ack_link_announce(struct virtnet_info *vi)
+{
+        rtnl_lock();
+        if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_ANNOUNCE,
+                                  VIRTIO_NET_CTRL_ANNOUNCE_ACK, NULL,
+                                  0, 0))
+                dev_warn(&vi->dev->dev, "Failed to ack link announce.\n");
+        rtnl_unlock();
+}
+
 static int virtnet_close(struct net_device *dev)
 {
         struct virtnet_info *vi = netdev_priv(dev);
@@ -951,20 +970,31 @@ static const struct net_device_ops virtnet_netdev = {
 #endif
 };
 
-static void virtnet_update_status(struct virtnet_info *vi)
+static void virtnet_config_changed_work(struct work_struct *work)
 {
+        struct virtnet_info *vi =
+                container_of(work, struct virtnet_info, config_work);
         u16 v;
 
+        mutex_lock(&vi->config_lock);
+        if (!vi->config_enable)
+                goto done;
+
         if (virtio_config_val(vi->vdev, VIRTIO_NET_F_STATUS,
                               offsetof(struct virtio_net_config, status),
                               &v) < 0)
-                return;
+                goto done;
+
+        if (v & VIRTIO_NET_S_ANNOUNCE) {
+                netif_notify_peers(vi->dev);
+                virtnet_ack_link_announce(vi);
+        }
 
         /* Ignore unknown (future) status bits */
         v &= VIRTIO_NET_S_LINK_UP;
 
         if (vi->status == v)
-                return;
+                goto done;
 
         vi->status = v;
 
@@ -975,13 +1005,15 @@ static void virtnet_update_status(struct virtnet_info *vi)
                 netif_carrier_off(vi->dev);
                 netif_stop_queue(vi->dev);
         }
+done:
+        mutex_unlock(&vi->config_lock);
 }
 
 static void virtnet_config_changed(struct virtio_device *vdev)
 {
         struct virtnet_info *vi = vdev->priv;
 
-        virtnet_update_status(vi);
+        queue_work(system_nrt_wq, &vi->config_work);
 }
 
 static int init_vqs(struct virtnet_info *vi)
@@ -1075,6 +1107,9 @@ static int virtnet_probe(struct virtio_device *vdev)
                 goto free;
 
         INIT_DELAYED_WORK(&vi->refill, refill_work);
+        mutex_init(&vi->config_lock);
+        vi->config_enable = true;
+        INIT_WORK(&vi->config_work, virtnet_config_changed_work);
         sg_init_table(vi->rx_sg, ARRAY_SIZE(vi->rx_sg));
         sg_init_table(vi->tx_sg, ARRAY_SIZE(vi->tx_sg));
 
@@ -1110,7 +1145,7 @@ static int virtnet_probe(struct virtio_device *vdev)
            otherwise get link status from config. */
         if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
                 netif_carrier_off(dev);
-                virtnet_update_status(vi);
+                queue_work(system_nrt_wq, &vi->config_work);
         } else {
                 vi->status = VIRTIO_NET_S_LINK_UP;
                 netif_carrier_on(dev);
@@ -1169,10 +1204,17 @@ static void __devexit virtnet_remove(struct virtio_device *vdev)
 {
         struct virtnet_info *vi = vdev->priv;
 
+        /* Prevent config work handler from accessing the device. */
+        mutex_lock(&vi->config_lock);
+        vi->config_enable = false;
+        mutex_unlock(&vi->config_lock);
+
         unregister_netdev(vi->dev);
 
         remove_vq_common(vi);
 
+        flush_work(&vi->config_work);
+
         free_percpu(vi->stats);
         free_netdev(vi->dev);
 }
@@ -1182,6 +1224,11 @@ static int virtnet_freeze(struct virtio_device *vdev)
 {
         struct virtnet_info *vi = vdev->priv;
 
+        /* Prevent config work handler from accessing the device */
+        mutex_lock(&vi->config_lock);
+        vi->config_enable = false;
+        mutex_unlock(&vi->config_lock);
+
         virtqueue_disable_cb(vi->rvq);
         virtqueue_disable_cb(vi->svq);
         if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ))
@@ -1195,6 +1242,8 @@ static int virtnet_freeze(struct virtio_device *vdev)
 
         remove_vq_common(vi);
 
+        flush_work(&vi->config_work);
+
         return 0;
 }
 
@@ -1215,6 +1264,10 @@ static int virtnet_restore(struct virtio_device *vdev)
         if (!try_fill_recv(vi, GFP_KERNEL))
                 queue_delayed_work(system_nrt_wq, &vi->refill, 0);
 
+        mutex_lock(&vi->config_lock);
+        vi->config_enable = true;
+        mutex_unlock(&vi->config_lock);
+
         return 0;
 }
 #endif
@@ -1232,6 +1285,7 @@ static unsigned int features[] = {
         VIRTIO_NET_F_GUEST_ECN, VIRTIO_NET_F_GUEST_UFO,
         VIRTIO_NET_F_MRG_RXBUF, VIRTIO_NET_F_STATUS, VIRTIO_NET_F_CTRL_VQ,
         VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN,
+        VIRTIO_NET_F_GUEST_ANNOUNCE,
 };
 
 static struct virtio_driver virtio_net_driver = {