Re: [PATCH v4 2/2] virtio_net: Extend virtio to use VF datapath when available

Samudrala, Sridhar
2018-03-12T20:58:06Z

On 3/12/2018 1:12 PM, Jiri Pirko wrote:
> Thu, Mar 01, 2018 at 09:08:43PM CET, sridhar.samudrala@intel.com wrote:
>> This patch enables virtio_net to switch over to a VF datapath when a VF
>> netdev is present with the same MAC address. It allows live migration
>> of a VM with a direct attached VF without the need to setup a bond/team
>> between a VF and virtio net device in the guest.
>>
>> The hypervisor needs to enable only one datapath at any time so that
>> packets don't get looped back to the VM over the other datapath. When a VF
>> is plugged, the virtio datapath link state can be marked as down. The
>> hypervisor needs to unplug the VF device from the guest on the source host
>> and reset the MAC filter of the VF to initiate failover of datapath to
>> virtio before starting the migration. After the migration is completed,
>> the destination hypervisor sets the MAC filter on the VF and plugs it back
>> to the guest to switch over to VF datapath.
>>
>> When BACKUP feature is enabled, an additional netdev(bypass netdev) is
>> created that acts as a master device and tracks the state of the 2 lower
>> netdevs. The original virtio_net netdev is marked as 'backup' netdev and a
>> passthru device with the same MAC is registered as 'active' netdev.
>>
>> This patch is based on the discussion initiated by Jesse on this thread.
>> https://marc.info/?l=linux-virtualization&m=151189725224231&w=2
>>
>> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
>> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
>> Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
> [...]
>
>
>> +static int virtnet_bypass_register_child(struct net_device *child_netdev)
>> +{
>> + struct virtnet_bypass_info *vbi;
>> + struct net_device *dev;
>> + bool backup;
>> + int ret;
>> +
>> + if (child_netdev->addr_len != ETH_ALEN)
>> + return NOTIFY_DONE;
>> +
>> + /* We will use the MAC address to locate the virtnet_bypass netdev
>> + * to associate with the child netdev. If we don't find a matching
>> + * bypass netdev, move on.
>> + */
>> + dev = get_virtnet_bypass_bymac(dev_net(child_netdev),
>> + child_netdev->perm_addr);
>> + if (!dev)
>> + return NOTIFY_DONE;
>> +
>> + vbi = netdev_priv(dev);
>> + backup = (child_netdev->dev.parent == dev->dev.parent);
>> + if (backup ? rtnl_dereference(vbi->backup_netdev) :
>> + rtnl_dereference(vbi->active_netdev)) {
>> + netdev_info(dev,
>> + "%s attempting to join bypass dev when %s already present\n",
>> + child_netdev->name, backup ? "backup" : "active");
>> + return NOTIFY_DONE;
>> + }
>> +
>> + /* Avoid non pci devices as active netdev */
>> + if (!backup && (!child_netdev->dev.parent ||
>> + !dev_is_pci(child_netdev->dev.parent)))
>> + return NOTIFY_DONE;
>> +
>> + ret = netdev_rx_handler_register(child_netdev,
>> + virtnet_bypass_handle_frame, dev);
>> + if (ret != 0) {
>> + netdev_err(child_netdev,
>> + "can not register bypass receive handler (err = %d)\n",
>> + ret);
>> + goto rx_handler_failed;
>> + }
>> +
>> + ret = netdev_upper_dev_link(child_netdev, dev, NULL);
>> + if (ret != 0) {
>> + netdev_err(child_netdev,
>> + "can not set master device %s (err = %d)\n",
>> + dev->name, ret);
>> + goto upper_link_failed;
>> + }
>> +
>> + child_netdev->flags |= IFF_SLAVE;
>> +
>> + if (netif_running(dev)) {
>> + ret = dev_open(child_netdev);
>> + if (ret && (ret != -EBUSY)) {
>> + netdev_err(dev, "Opening child %s failed ret:%d\n",
>> + child_netdev->name, ret);
>> + goto err_interface_up;
>> + }
>> + }
> Much of this function is copy of netvsc_vf_join, should be shared with
> netvsc.

Yes. This is based on netvsc_register_vf() and netvsc_vf_join(). But modified
to handle registration of 2 child netdevs(backup virtio and active vf).  In case
of netvsc, they only register VF. There is no backup netdev.
I think trying to make this code shareable with netvsc will introduce additional
checks and make it convoluted.

>
>
>> +
>> + /* Align MTU of child with master */
>> + ret = dev_set_mtu(child_netdev, dev->mtu);
>> + if (ret) {
>> + netdev_err(dev,
>> + "unable to change mtu of %s to %u register failed\n",
>> + child_netdev->name, dev->mtu);
>> + goto err_set_mtu;
>> + }
>> +
>> + call_netdevice_notifiers(NETDEV_JOIN, child_netdev);
>> +
>> + netdev_info(dev, "registering %s\n", child_netdev->name);
>> +
>> + dev_hold(child_netdev);
>> + if (backup) {
>> + rcu_assign_pointer(vbi->backup_netdev, child_netdev);
>> + dev_get_stats(vbi->backup_netdev, &vbi->backup_stats);
>> + } else {
>> + rcu_assign_pointer(vbi->active_netdev, child_netdev);
>> + dev_get_stats(vbi->active_netdev, &vbi->active_stats);
>> + dev->min_mtu = child_netdev->min_mtu;
>> + dev->max_mtu = child_netdev->max_mtu;
>> + }
>> +
>> + return NOTIFY_OK;
>> +
>> +err_set_mtu:
>> + dev_close(child_netdev);
>> +err_interface_up:
>> + netdev_upper_dev_unlink(child_netdev, dev);
>> + child_netdev->flags &= ~IFF_SLAVE;
>> +upper_link_failed:
>> + netdev_rx_handler_unregister(child_netdev);
>> +rx_handler_failed:
>> + return NOTIFY_DONE;
>> +}
>> +
>> +static int virtnet_bypass_unregister_child(struct net_device *child_netdev)
>> +{
>> + struct virtnet_bypass_info *vbi;
>> + struct net_device *dev, *backup;
>> +
>> + dev = get_virtnet_bypass_byref(child_netdev);
>> + if (!dev)
>> + return NOTIFY_DONE;
>> +
>> + vbi = netdev_priv(dev);
>> +
>> + netdev_info(dev, "unregistering %s\n", child_netdev->name);
>> +
>> + netdev_rx_handler_unregister(child_netdev);
>> + netdev_upper_dev_unlink(child_netdev, dev);
>> + child_netdev->flags &= ~IFF_SLAVE;
>> +
>> + if (child_netdev->dev.parent == dev->dev.parent) {
>> + RCU_INIT_POINTER(vbi->backup_netdev, NULL);
>> + } else {
>> + RCU_INIT_POINTER(vbi->active_netdev, NULL);
>> + backup = rtnl_dereference(vbi->backup_netdev);
>> + if (backup) {
>> + dev->min_mtu = backup->min_mtu;
>> + dev->max_mtu = backup->max_mtu;
>> + }
>> + }
>> +
>> + dev_put(child_netdev);
>> +
>> + return NOTIFY_OK;
>> +}
>> +
>> +static int virtnet_bypass_update_link(struct net_device *child_netdev)
>> +{
>> + struct net_device *dev, *active, *backup;
>> + struct virtnet_bypass_info *vbi;
>> +
>> + dev = get_virtnet_bypass_byref(child_netdev);
>> + if (!dev || !netif_running(dev))
>> + return NOTIFY_DONE;
>> +
>> + vbi = netdev_priv(dev);
>> +
>> + active = rtnl_dereference(vbi->active_netdev);
>> + backup = rtnl_dereference(vbi->backup_netdev);
>> +
>> + if ((active && virtnet_bypass_xmit_ready(active)) ||
>> + (backup && virtnet_bypass_xmit_ready(backup))) {
>> + netif_carrier_on(dev);
>> + netif_tx_wake_all_queues(dev);
>> + } else {
>> + netif_carrier_off(dev);
>> + netif_tx_stop_all_queues(dev);
>> + }
>> +
>> + return NOTIFY_OK;
>> +}
>> +
>> +static int virtnet_bypass_event(struct notifier_block *this,
>> + unsigned long event, void *ptr)
>> +{
>> + struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
>> +
>> + /* Skip our own events */
>> + if (event_dev->netdev_ops == &virtnet_bypass_netdev_ops)
>> + return NOTIFY_DONE;
>> +
>> + /* Avoid non-Ethernet type devices */
>> + if (event_dev->type != ARPHRD_ETHER)
>> + return NOTIFY_DONE;
>> +
>> + /* Avoid Vlan dev with same MAC registering as child dev */
>> + if (is_vlan_dev(event_dev))
>> + return NOTIFY_DONE;
>> +
>> + /* Avoid Bonding master dev with same MAC registering as child dev */
>> + if ((event_dev->priv_flags & IFF_BONDING) &&
>> + (event_dev->flags & IFF_MASTER))
>> + return NOTIFY_DONE;
>> +
>> + switch (event) {
>> + case NETDEV_REGISTER:
>> + return virtnet_bypass_register_child(event_dev);
>> + case NETDEV_UNREGISTER:
>> + return virtnet_bypass_unregister_child(event_dev);
>> + case NETDEV_UP:
>> + case NETDEV_DOWN:
>> + case NETDEV_CHANGE:
>> + return virtnet_bypass_update_link(event_dev);
>> + default:
>> + return NOTIFY_DONE;
>> + }
>> +}
> For example this function is 1:1 copy of netvsc, even with comments
> and bugs (like IFF_BODING check).
>
> This is also something that should be shared with netvsc.

The problem is with the calls that are made from this function.
Sharing would have been possible if both virtio and netvsc went with
same netdev model.

>
>
>> +
>> +static struct notifier_block virtnet_bypass_notifier = {
>> + .notifier_call = virtnet_bypass_event,
>> +};
>> +
>> +static int virtnet_bypass_create(struct virtnet_info *vi)
>> +{
>> + struct net_device *backup_netdev = vi->dev;
>> + struct device *dev = &vi->vdev->dev;
>> + struct net_device *bypass_netdev;
>> + int res;
>> +
>> + /* Alloc at least 2 queues, for now we are going with 16 assuming
>> + * that most devices being bonded won't have too many queues.
>> + */
>> + bypass_netdev = alloc_etherdev_mq(sizeof(struct virtnet_bypass_info),
>> + 16);
>> + if (!bypass_netdev) {
>> + dev_err(dev, "Unable to allocate bypass_netdev!\n");
>> + return -ENOMEM;
>> + }
>> +
>> + dev_net_set(bypass_netdev, dev_net(backup_netdev));
>> + SET_NETDEV_DEV(bypass_netdev, dev);
>> +
>> + bypass_netdev->netdev_ops = &virtnet_bypass_netdev_ops;
>> + bypass_netdev->ethtool_ops = &virtnet_bypass_ethtool_ops;
>> +
>> + /* Initialize the device options */
>> + bypass_netdev->flags |= IFF_MASTER;
>> + bypass_netdev->priv_flags |= IFF_BONDING | IFF_UNICAST_FLT |
> No clue why you set IFF_BONDING here...

This is to indicate to the userspace that this is a master bond device.
May be it is sufficient to just set IFF_MASTER.

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