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

Samudrala, Sridhar
2018-03-14T00:36:23Z

On 3/12/2018 2:08 PM, Jiri Pirko wrote:
> Mon, Mar 12, 2018 at 09:58:06PM CET, sridhar.samudrala@intel.com wrote:
>>
>> 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.
> No problem.

Not clear what you meant here?
Want to confirm that you are agreeing that it is OK to not share this function
with netvsc.

>
>
>>
>>>
>>>> +
>>>> + /* 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.
> ops? You can still share.

OK. looks like you want to see atleast some code shared between netvsc and virtio_net
even when they are using 2 different netdev models.
Will try to add a new file under net/core and move some functions that can be shared
between netvsc and virtio_net in BACKUP mode.

>
>
>>>
>>>> +
>>>> +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.
> This is not a master bond device! If you say this, it makes me really
> worried....
>
Will remove IFF_BONDING in the next revision.

>
>> May be it is sufficient to just set IFF_MASTER.
>>
>>>
>>>
>>>
>>>