Linux Virtualization - Jan 2018 - [RFC PATCH net-next v2 0/2] Enable virtio to act as a backup for a passthru device

This patch series extends virtio_net to take over VF datapath by
simulating a transparent bond without creating any additional netdev.

I understand that there are some comments suggesting an alternate model
that is based on 3 driver model(virtio_net, VF driver, a new driver 
virt_bond that acts as a master to virtio_net and VF).

Would like to get some feedback on the right way to solve the live
migration problem with direct attached devices in KVM environment.

Stephen,
Is the netvsc transparent bond implemenation robust enough and deployed
in real environments? Or would netvsc switch over to a 3-driver model if
that solution becomes available?

Can we start with this implementation that is similar to netvsc and if
needed we can move to the 3 driver model later?

This patch series enables virtio 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 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.

It is based on netvsc implementation and it should be possible to make this
code generic and move it to a common location that can be shared by netvsc
and virtio.

This patch series is based on the discussion initiated by Jesse on this thread.
https://marc.info/?l=linux-virtualization&m=151189725224231&w=2

v2:
- Changed VIRTIO_NET_F_MASTER to VIRTIO_NET_F_BACKUP (mst)
- made a small change to the virtio-net xmit path to only use VF datapath
  for unicasts. Broadcasts/multicasts use virtio datapath. This avoids
  east-west broadcasts to go over the PCI link.
- added suppport for the feature bit in qemu

Sridhar Samudrala (2):
  virtio_net: Introduce VIRTIO_NET_F_BACKUP feature bit
  virtio_net: Extend virtio to use VF datapath when available

 drivers/net/virtio_net.c        | 309 +++++++++++++++++++++++++++++++++++++++-
 include/uapi/linux/virtio_net.h |   3 +
 2 files changed, 309 insertions(+), 3 deletions(-)

Sridhar Samudrala (1):
  qemu: Introduce VIRTIO_NET_F_BACKUP feature bit to virtio_net

 hw/net/virtio-net.c                         | 2 ++
 include/standard-headers/linux/virtio_net.h | 3 +++
 2 files changed, 5 insertions(+)

-- 
2.14.3

This feature bit can be used by hypervisor to indicate virtio_net device to
act as a backup for another device with the same MAC address.

Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
---
 drivers/net/virtio_net.c        | 2 +-
 include/uapi/linux/virtio_net.h | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 12dfc5fee58e..f149a160a8c5 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2829,7 +2829,7 @@ static struct virtio_device_id id_table[] = {
 	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
 	VIRTIO_NET_F_CTRL_MAC_ADDR, \
 	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \
-	VIRTIO_NET_F_SPEED_DUPLEX
+	VIRTIO_NET_F_SPEED_DUPLEX, VIRTIO_NET_F_BACKUP
 
 static unsigned int features[] = {
 	VIRTNET_FEATURES,
diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index 5de6ed37695b..c7c35fd1a5ed 100644
--- a/include/uapi/linux/virtio_net.h
+++ b/include/uapi/linux/virtio_net.h
@@ -57,6 +57,9 @@
 					 * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
 
+#define VIRTIO_NET_F_BACKUP	  62	/* Act as backup for another device
+					 * with the same MAC.
+					 */
 #define VIRTIO_NET_F_SPEED_DUPLEX 63	/* Device set linkspeed and duplex */
 
 #ifndef VIRTIO_NET_NO_LEGACY
-- 
2.14.3

This patch enables virtio_net to switch over to a VF datapath when a VF
netdev is present with the same MAC address. The VF datapath is only used
for unicast traffic. Broadcasts/multicasts go via virtio datapath so that
east-west broadcasts don't use the PCI bandwidth. 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 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.

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 at intel.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg at intel.com>
---
 drivers/net/virtio_net.c | 307 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 305 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index f149a160a8c5..0e58d364fde9 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -30,6 +30,8 @@
 #include <linux/cpu.h>
 #include <linux/average.h>
 #include <linux/filter.h>
+#include <linux/netdevice.h>
+#include <linux/netpoll.h>
 #include <net/route.h>
 #include <net/xdp.h>
 
@@ -120,6 +122,15 @@ struct receive_queue {
 	struct xdp_rxq_info xdp_rxq;
 };
 
+struct virtnet_vf_pcpu_stats {
+	u64	rx_packets;
+	u64	rx_bytes;
+	u64	tx_packets;
+	u64	tx_bytes;
+	struct u64_stats_sync   syncp;
+	u32	tx_dropped;
+};
+
 struct virtnet_info {
 	struct virtio_device *vdev;
 	struct virtqueue *cvq;
@@ -182,6 +193,10 @@ struct virtnet_info {
 	u32 speed;
 
 	unsigned long guest_offloads;
+
+	/* State to manage the associated VF interface. */
+	struct net_device __rcu *vf_netdev;
+	struct virtnet_vf_pcpu_stats __percpu *vf_stats;
 };
 
 struct padded_vnet_hdr {
@@ -1314,16 +1329,53 @@ static int xmit_skb(struct send_queue *sq, struct
sk_buff *skb)
 	return virtqueue_add_outbuf(sq->vq, sq->sg, num_sg, skb, GFP_ATOMIC);
 }
 
+/* Send skb on the slave VF device. */
+static int virtnet_vf_xmit(struct net_device *dev, struct net_device
*vf_netdev,
+			   struct sk_buff *skb)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+	unsigned int len = skb->len;
+	int rc;
+
+	skb->dev = vf_netdev;
+	skb->queue_mapping = qdisc_skb_cb(skb)->slave_dev_queue_mapping;
+
+	rc = dev_queue_xmit(skb);
+	if (likely(rc == NET_XMIT_SUCCESS || rc == NET_XMIT_CN)) {
+		struct virtnet_vf_pcpu_stats *pcpu_stats
+			= this_cpu_ptr(vi->vf_stats);
+
+		u64_stats_update_begin(&pcpu_stats->syncp);
+		pcpu_stats->tx_packets++;
+		pcpu_stats->tx_bytes += len;
+		u64_stats_update_end(&pcpu_stats->syncp);
+	} else {
+		this_cpu_inc(vi->vf_stats->tx_dropped);
+	}
+
+	return rc;
+}
+
 static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
 	int qnum = skb_get_queue_mapping(skb);
 	struct send_queue *sq = &vi->sq[qnum];
+	struct net_device *vf_netdev;
 	int err;
 	struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
 	bool kick = !skb->xmit_more;
 	bool use_napi = sq->napi.weight;
 
+	/* If VF is present and up then redirect packets
+	 * called with rcu_read_lock_bh
+	 */
+	vf_netdev = rcu_dereference_bh(vi->vf_netdev);
+	if (vf_netdev && netif_running(vf_netdev) &&
+	    !netpoll_tx_running(dev) &&
+	    is_unicast_ether_addr(eth_hdr(skb)->h_dest))
+		return virtnet_vf_xmit(dev, vf_netdev, skb);
+
 	/* Free up any pending old buffers before queueing new ones. */
 	free_old_xmit_skbs(sq);
 
@@ -1470,10 +1522,41 @@ static int virtnet_set_mac_address(struct net_device
*dev, void *p)
 	return ret;
 }
 
+static void virtnet_get_vf_stats(struct net_device *dev,
+				 struct virtnet_vf_pcpu_stats *tot)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+	int i;
+
+	memset(tot, 0, sizeof(*tot));
+
+	for_each_possible_cpu(i) {
+		const struct virtnet_vf_pcpu_stats *stats
+				= per_cpu_ptr(vi->vf_stats, i);
+		u64 rx_packets, rx_bytes, tx_packets, tx_bytes;
+		unsigned int start;
+
+		do {
+			start = u64_stats_fetch_begin_irq(&stats->syncp);
+			rx_packets = stats->rx_packets;
+			tx_packets = stats->tx_packets;
+			rx_bytes = stats->rx_bytes;
+			tx_bytes = stats->tx_bytes;
+		} while (u64_stats_fetch_retry_irq(&stats->syncp, start));
+
+		tot->rx_packets += rx_packets;
+		tot->tx_packets += tx_packets;
+		tot->rx_bytes   += rx_bytes;
+		tot->tx_bytes   += tx_bytes;
+		tot->tx_dropped += stats->tx_dropped;
+	}
+}
+
 static void virtnet_stats(struct net_device *dev,
 			  struct rtnl_link_stats64 *tot)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
+	struct virtnet_vf_pcpu_stats vf_stats;
 	int cpu;
 	unsigned int start;
 
@@ -1504,6 +1587,13 @@ static void virtnet_stats(struct net_device *dev,
 	tot->rx_dropped = dev->stats.rx_dropped;
 	tot->rx_length_errors = dev->stats.rx_length_errors;
 	tot->rx_frame_errors = dev->stats.rx_frame_errors;
+
+	virtnet_get_vf_stats(dev, &vf_stats);
+	tot->rx_packets += vf_stats.rx_packets;
+	tot->tx_packets += vf_stats.tx_packets;
+	tot->rx_bytes += vf_stats.rx_bytes;
+	tot->tx_bytes += vf_stats.tx_bytes;
+	tot->tx_dropped += vf_stats.tx_dropped;
 }
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
@@ -2635,6 +2725,13 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
 
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_BACKUP)) {
+		vi->vf_stats +			netdev_alloc_pcpu_stats(struct virtnet_vf_pcpu_stats);
+		if (!vi->vf_stats)
+			goto free_stats;
+	}
+
 	/* If we can receive ANY GSO packets, we must allocate large ones. */
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
 	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6) ||
@@ -2668,7 +2765,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 			 */
 			dev_err(&vdev->dev, "device MTU appears to have changed "
 				"it is now %d < %d", mtu, dev->min_mtu);
-			goto free_stats;
+			goto free_vf_stats;
 		}
 
 		dev->mtu = mtu;
@@ -2692,7 +2789,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 	/* Allocate/initialize the rx/tx queues, and invoke find_vqs */
 	err = init_vqs(vi);
 	if (err)
-		goto free_stats;
+		goto free_vf_stats;
 
 #ifdef CONFIG_SYSFS
 	if (vi->mergeable_rx_bufs)
@@ -2747,6 +2844,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 	cancel_delayed_work_sync(&vi->refill);
 	free_receive_page_frags(vi);
 	virtnet_del_vqs(vi);
+free_vf_stats:
+	free_percpu(vi->vf_stats);
 free_stats:
 	free_percpu(vi->stats);
 free:
@@ -2768,19 +2867,184 @@ static void remove_vq_common(struct virtnet_info *vi)
 	virtnet_del_vqs(vi);
 }
 
+static struct net_device *get_virtio_bymac(const u8 *mac)
+{
+	struct net_device *dev;
+
+	ASSERT_RTNL();
+
+	for_each_netdev(&init_net, dev) {
+		if (dev->netdev_ops != &virtnet_netdev)
+			continue;       /* not a virtio_net device */
+
+		if (ether_addr_equal(mac, dev->perm_addr))
+			return dev;
+	}
+
+	return NULL;
+}
+
+static struct net_device *get_virtio_byref(struct net_device *vf_netdev)
+{
+	struct net_device *dev;
+
+	ASSERT_RTNL();
+
+	for_each_netdev(&init_net, dev) {
+		struct virtnet_info *vi;
+
+		if (dev->netdev_ops != &virtnet_netdev)
+			continue;	/* not a virtio_net device */
+
+		vi = netdev_priv(dev);
+		if (rtnl_dereference(vi->vf_netdev) == vf_netdev)
+			return dev;	/* a match */
+	}
+
+	return NULL;
+}
+
+/* Called when VF is injecting data into network stack.
+ * Change the associated network device from VF to virtio.
+ * note: already called with rcu_read_lock
+ */
+static rx_handler_result_t virtnet_vf_handle_frame(struct sk_buff **pskb)
+{
+	struct sk_buff *skb = *pskb;
+	struct net_device *ndev = rcu_dereference(skb->dev->rx_handler_data);
+	struct virtnet_info *vi = netdev_priv(ndev);
+	struct virtnet_vf_pcpu_stats *pcpu_stats +				this_cpu_ptr(vi->vf_stats);
+
+	skb->dev = ndev;
+
+	u64_stats_update_begin(&pcpu_stats->syncp);
+	pcpu_stats->rx_packets++;
+	pcpu_stats->rx_bytes += skb->len;
+	u64_stats_update_end(&pcpu_stats->syncp);
+
+	return RX_HANDLER_ANOTHER;
+}
+
+static int virtnet_vf_join(struct net_device *vf_netdev,
+			   struct net_device *ndev)
+{
+	int ret;
+
+	ret = netdev_rx_handler_register(vf_netdev,
+					 virtnet_vf_handle_frame, ndev);
+	if (ret != 0) {
+		netdev_err(vf_netdev,
+			   "can not register virtio VF receive handler (err = %d)\n",
+			   ret);
+		goto rx_handler_failed;
+	}
+
+	ret = netdev_upper_dev_link(vf_netdev, ndev, NULL);
+	if (ret != 0) {
+		netdev_err(vf_netdev,
+			   "can not set master device %s (err = %d)\n",
+			   ndev->name, ret);
+		goto upper_link_failed;
+	}
+
+	vf_netdev->flags |= IFF_SLAVE;
+
+	/* Align MTU of VF with master */
+	ret = dev_set_mtu(vf_netdev, ndev->mtu);
+	if (ret)
+		netdev_warn(vf_netdev,
+			    "unable to change mtu to %u\n", ndev->mtu);
+
+	call_netdevice_notifiers(NETDEV_JOIN, vf_netdev);
+
+	netdev_info(vf_netdev, "joined to %s\n", ndev->name);
+	return 0;
+
+upper_link_failed:
+	netdev_rx_handler_unregister(vf_netdev);
+rx_handler_failed:
+	return ret;
+}
+
+static int virtnet_register_vf(struct net_device *vf_netdev)
+{
+	struct net_device *ndev;
+	struct virtnet_info *vi;
+
+	if (vf_netdev->addr_len != ETH_ALEN)
+		return NOTIFY_DONE;
+
+	/* We will use the MAC address to locate the virtio_net interface to
+	 * associate with the VF interface. If we don't find a matching
+	 * virtio interface, move on.
+	 */
+	ndev = get_virtio_bymac(vf_netdev->perm_addr);
+	if (!ndev)
+		return NOTIFY_DONE;
+
+	vi = netdev_priv(ndev);
+	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_BACKUP))
+		return NOTIFY_DONE;
+
+	if (rtnl_dereference(vi->vf_netdev))
+		return NOTIFY_DONE;
+
+	if (virtnet_vf_join(vf_netdev, ndev) != 0)
+		return NOTIFY_DONE;
+
+	netdev_info(ndev, "VF registering %s\n", vf_netdev->name);
+
+	dev_hold(vf_netdev);
+	rcu_assign_pointer(vi->vf_netdev, vf_netdev);
+
+	return NOTIFY_OK;
+}
+
+static int virtnet_unregister_vf(struct net_device *vf_netdev)
+{
+	struct net_device *ndev;
+	struct virtnet_info *vi;
+
+	ndev = get_virtio_byref(vf_netdev);
+	if (!ndev)
+		return NOTIFY_DONE;
+
+	vi = netdev_priv(ndev);
+	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_BACKUP))
+		return NOTIFY_DONE;
+
+	netdev_info(ndev, "VF unregistering %s\n", vf_netdev->name);
+
+	netdev_rx_handler_unregister(vf_netdev);
+	netdev_upper_dev_unlink(vf_netdev, ndev);
+	RCU_INIT_POINTER(vi->vf_netdev, NULL);
+	dev_put(vf_netdev);
+
+	return NOTIFY_OK;
+}
+
 static void virtnet_remove(struct virtio_device *vdev)
 {
 	struct virtnet_info *vi = vdev->priv;
+	struct net_device *vf_netdev;
 
 	virtnet_cpu_notif_remove(vi);
 
 	/* Make sure no work handler is accessing the device. */
 	flush_work(&vi->config_work);
 
+	rtnl_lock();
+	vf_netdev = rtnl_dereference(vi->vf_netdev);
+	if (vf_netdev)
+		virtnet_unregister_vf(vf_netdev);
+	rtnl_unlock();
+
 	unregister_netdev(vi->dev);
 
 	remove_vq_common(vi);
 
+	free_percpu(vi->vf_stats);
 	free_percpu(vi->stats);
 	free_netdev(vi->dev);
 }
@@ -2859,6 +3123,42 @@ static struct virtio_driver virtio_net_driver = {
 #endif
 };
 
+static int virtio_netdev_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_netdev)
+		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 VF */
+	if (is_vlan_dev(event_dev))
+		return NOTIFY_DONE;
+
+	/* Avoid Bonding master dev with same MAC registering as VF */
+	if ((event_dev->priv_flags & IFF_BONDING) &&
+	    (event_dev->flags & IFF_MASTER))
+		return NOTIFY_DONE;
+
+	switch (event) {
+	case NETDEV_REGISTER:
+		return virtnet_register_vf(event_dev);
+	case NETDEV_UNREGISTER:
+		return virtnet_unregister_vf(event_dev);
+	default:
+		return NOTIFY_DONE;
+	}
+}
+
+static struct notifier_block virtio_netdev_notifier = {
+	.notifier_call = virtio_netdev_event,
+};
+
 static __init int virtio_net_driver_init(void)
 {
 	int ret;
@@ -2877,6 +3177,8 @@ static __init int virtio_net_driver_init(void)
         ret = register_virtio_driver(&virtio_net_driver);
 	if (ret)
 		goto err_virtio;
+
+	register_netdevice_notifier(&virtio_netdev_notifier);
 	return 0;
 err_virtio:
 	cpuhp_remove_multi_state(CPUHP_VIRT_NET_DEAD);
@@ -2889,6 +3191,7 @@ module_init(virtio_net_driver_init);
 
 static __exit void virtio_net_driver_exit(void)
 {
+	unregister_netdevice_notifier(&virtio_netdev_notifier);
 	unregister_virtio_driver(&virtio_net_driver);
 	cpuhp_remove_multi_state(CPUHP_VIRT_NET_DEAD);
 	cpuhp_remove_multi_state(virtionet_online);
-- 
2.14.3

This feature bit can be used by hypervisor to indicate virtio_net device to
act as a backup for another device with the same MAC address.
    
Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index cd63659140..fa47e723b9 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -2193,6 +2193,8 @@ static Property virtio_net_properties[] = {
                      true),
     DEFINE_PROP_INT32("speed", VirtIONet, net_conf.speed,
SPEED_UNKNOWN),
     DEFINE_PROP_STRING("duplex", VirtIONet, net_conf.duplex_str),
+    DEFINE_PROP_BIT64("backup", VirtIONet, host_features,
+                    VIRTIO_NET_F_BACKUP, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/include/standard-headers/linux/virtio_net.h
b/include/standard-headers/linux/virtio_net.h
index 17c8531a22..6afca6dcaf 100644
--- a/include/standard-headers/linux/virtio_net.h
+++ b/include/standard-headers/linux/virtio_net.h
@@ -57,6 +57,9 @@
 					 * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
 
+#define VIRTIO_NET_F_BACKUP	  62   /* Act as backup for another device
+					* with the same MAC.
+					*/
 #define VIRTIO_NET_F_SPEED_DUPLEX 63   /* Device set linkspeed and duplex */
 
 #ifndef VIRTIO_NET_NO_LEGACY

On Thu, Jan 11, 2018 at 9:58 PM, Sridhar Samudrala
<sridhar.samudrala at intel.com> wrote:
> This feature bit can be used by hypervisor to indicate virtio_net device to
> act as a backup for another device with the same MAC address.
>
> Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
> ---
>  drivers/net/virtio_net.c        | 2 +-
>  include/uapi/linux/virtio_net.h | 3 +++
>  2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 12dfc5fee58e..f149a160a8c5 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2829,7 +2829,7 @@ static struct virtio_device_id id_table[] = {
>         VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
>         VIRTIO_NET_F_CTRL_MAC_ADDR, \
>         VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \
> -       VIRTIO_NET_F_SPEED_DUPLEX
> +       VIRTIO_NET_F_SPEED_DUPLEX, VIRTIO_NET_F_BACKUP
>
>  static unsigned int features[] = {
>         VIRTNET_FEATURES,
> diff --git a/include/uapi/linux/virtio_net.h
b/include/uapi/linux/virtio_net.h
> index 5de6ed37695b..c7c35fd1a5ed 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -57,6 +57,9 @@
>                                          * Steering */
>  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23  /* Set MAC address */
>
> +#define VIRTIO_NET_F_BACKUP      62    /* Act as backup for another device
> +                                        * with the same MAC.
> +                                        */
>  #define VIRTIO_NET_F_SPEED_DUPLEX 63   /* Device set linkspeed and duplex
*/
>
>  #ifndef VIRTIO_NET_NO_LEGACY
I'm not a huge fan of the name "backup" since that implies that
the
Virtio interface is only used if the VF is not present, and there are
multiple instances such as dealing with east/west or
broadcast/multicast traffic where it may be desirable to use the
para-virtual interface rather then deal with PCI overhead/bottleneck
to send the packet.

What if instead of BACKUP we used the name SIDE_CHANNEL? Basically it
is a bit of double entendre as we are using the physical MAC address
to provide configuration information, and then in addition this
interface acts as a secondary channel for passing frames to and from
the guest rather than just using the VF.

Just a thought.

Thanks.

- Alex

First off, as mentioned in another thread, the model of stacking up
virt-bond functionality over virtio seems a wrong direction to me.
Essentially the migration process would need to carry over all guest
side configurations previously done on the VF/PT and get them moved to
the new device being it virtio or VF/PT. Without the help of a new
upper layer bond driver that enslaves virtio and VF/PT devices
underneath, virtio will be overloaded with too much specifics being a
VF/PT backup in the future. I hope you're already aware of the issue
in longer term and move to that model as soon as possible. See more
inline.

On Thu, Jan 11, 2018 at 9:58 PM, Sridhar Samudrala
<sridhar.samudrala at 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. The VF datapath is only used
> for unicast traffic. Broadcasts/multicasts go via virtio datapath so that
> east-west broadcasts don't use the PCI bandwidth.
Why not making an this an option/optimization rather than being the
only means? The problem of east-west broadcast eating PCI bandwidth
depends on specifics of the (virtual) network setup, while some users
won't want to lose VF's merits such as latency. Why restricting
broadcast/multicast xmit to virtio only which potentially regresses
the performance against raw VF?
> 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 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.
Is there a host side patch (planned) for this MAC filter switching
process? As said in another thread, that simple script won't work for
macvtap backend.

Thanks,
-Siwei
>
> 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 at intel.com>
> Reviewed-by: Jesse Brandeburg <jesse.brandeburg at intel.com>
> ---
>  drivers/net/virtio_net.c | 307
++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 305 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index f149a160a8c5..0e58d364fde9 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -30,6 +30,8 @@
>  #include <linux/cpu.h>
>  #include <linux/average.h>
>  #include <linux/filter.h>
> +#include <linux/netdevice.h>
> +#include <linux/netpoll.h>
>  #include <net/route.h>
>  #include <net/xdp.h>
>
> @@ -120,6 +122,15 @@ struct receive_queue {
>         struct xdp_rxq_info xdp_rxq;
>  };
>
> +struct virtnet_vf_pcpu_stats {
> +       u64     rx_packets;
> +       u64     rx_bytes;
> +       u64     tx_packets;
> +       u64     tx_bytes;
> +       struct u64_stats_sync   syncp;
> +       u32     tx_dropped;
> +};
> +
>  struct virtnet_info {
>         struct virtio_device *vdev;
>         struct virtqueue *cvq;
> @@ -182,6 +193,10 @@ struct virtnet_info {
>         u32 speed;
>
>         unsigned long guest_offloads;
> +
> +       /* State to manage the associated VF interface. */
> +       struct net_device __rcu *vf_netdev;
> +       struct virtnet_vf_pcpu_stats __percpu *vf_stats;
>  };
>
>  struct padded_vnet_hdr {
> @@ -1314,16 +1329,53 @@ static int xmit_skb(struct send_queue *sq, struct
sk_buff *skb)
>         return virtqueue_add_outbuf(sq->vq, sq->sg, num_sg, skb,
GFP_ATOMIC);
>  }
>
> +/* Send skb on the slave VF device. */
> +static int virtnet_vf_xmit(struct net_device *dev, struct net_device
*vf_netdev,
> +                          struct sk_buff *skb)
> +{
> +       struct virtnet_info *vi = netdev_priv(dev);
> +       unsigned int len = skb->len;
> +       int rc;
> +
> +       skb->dev = vf_netdev;
> +       skb->queue_mapping =
qdisc_skb_cb(skb)->slave_dev_queue_mapping;
> +
> +       rc = dev_queue_xmit(skb);
> +       if (likely(rc == NET_XMIT_SUCCESS || rc == NET_XMIT_CN)) {
> +               struct virtnet_vf_pcpu_stats *pcpu_stats
> +                       = this_cpu_ptr(vi->vf_stats);
> +
> +               u64_stats_update_begin(&pcpu_stats->syncp);
> +               pcpu_stats->tx_packets++;
> +               pcpu_stats->tx_bytes += len;
> +               u64_stats_update_end(&pcpu_stats->syncp);
> +       } else {
> +               this_cpu_inc(vi->vf_stats->tx_dropped);
> +       }
> +
> +       return rc;
> +}
> +
>  static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>  {
>         struct virtnet_info *vi = netdev_priv(dev);
>         int qnum = skb_get_queue_mapping(skb);
>         struct send_queue *sq = &vi->sq[qnum];
> +       struct net_device *vf_netdev;
>         int err;
>         struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
>         bool kick = !skb->xmit_more;
>         bool use_napi = sq->napi.weight;
>
> +       /* If VF is present and up then redirect packets
> +        * called with rcu_read_lock_bh
> +        */
> +       vf_netdev = rcu_dereference_bh(vi->vf_netdev);
> +       if (vf_netdev && netif_running(vf_netdev) &&
> +           !netpoll_tx_running(dev) &&
> +           is_unicast_ether_addr(eth_hdr(skb)->h_dest))
> +               return virtnet_vf_xmit(dev, vf_netdev, skb);
> +
>         /* Free up any pending old buffers before queueing new ones. */
>         free_old_xmit_skbs(sq);
>
> @@ -1470,10 +1522,41 @@ static int virtnet_set_mac_address(struct
net_device *dev, void *p)
>         return ret;
>  }
>
> +static void virtnet_get_vf_stats(struct net_device *dev,
> +                                struct virtnet_vf_pcpu_stats *tot)
> +{
> +       struct virtnet_info *vi = netdev_priv(dev);
> +       int i;
> +
> +       memset(tot, 0, sizeof(*tot));
> +
> +       for_each_possible_cpu(i) {
> +               const struct virtnet_vf_pcpu_stats *stats
> +                               = per_cpu_ptr(vi->vf_stats, i);
> +               u64 rx_packets, rx_bytes, tx_packets, tx_bytes;
> +               unsigned int start;
> +
> +               do {
> +                       start =
u64_stats_fetch_begin_irq(&stats->syncp);
> +                       rx_packets = stats->rx_packets;
> +                       tx_packets = stats->tx_packets;
> +                       rx_bytes = stats->rx_bytes;
> +                       tx_bytes = stats->tx_bytes;
> +               } while (u64_stats_fetch_retry_irq(&stats->syncp,
start));
> +
> +               tot->rx_packets += rx_packets;
> +               tot->tx_packets += tx_packets;
> +               tot->rx_bytes   += rx_bytes;
> +               tot->tx_bytes   += tx_bytes;
> +               tot->tx_dropped += stats->tx_dropped;
> +       }
> +}
> +
>  static void virtnet_stats(struct net_device *dev,
>                           struct rtnl_link_stats64 *tot)
>  {
>         struct virtnet_info *vi = netdev_priv(dev);
> +       struct virtnet_vf_pcpu_stats vf_stats;
>         int cpu;
>         unsigned int start;
>
> @@ -1504,6 +1587,13 @@ static void virtnet_stats(struct net_device *dev,
>         tot->rx_dropped = dev->stats.rx_dropped;
>         tot->rx_length_errors = dev->stats.rx_length_errors;
>         tot->rx_frame_errors = dev->stats.rx_frame_errors;
> +
> +       virtnet_get_vf_stats(dev, &vf_stats);
> +       tot->rx_packets += vf_stats.rx_packets;
> +       tot->tx_packets += vf_stats.tx_packets;
> +       tot->rx_bytes += vf_stats.rx_bytes;
> +       tot->tx_bytes += vf_stats.tx_bytes;
> +       tot->tx_dropped += vf_stats.tx_dropped;
>  }
>
>  #ifdef CONFIG_NET_POLL_CONTROLLER
> @@ -2635,6 +2725,13 @@ static int virtnet_probe(struct virtio_device *vdev)
>
>         INIT_WORK(&vi->config_work, virtnet_config_changed_work);
>
> +       if (virtio_has_feature(vdev, VIRTIO_NET_F_BACKUP)) {
> +               vi->vf_stats > +                      
netdev_alloc_pcpu_stats(struct virtnet_vf_pcpu_stats);
> +               if (!vi->vf_stats)
> +                       goto free_stats;
> +       }
> +
>         /* If we can receive ANY GSO packets, we must allocate large ones.
*/
>         if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
>             virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6) ||
> @@ -2668,7 +2765,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>                          */
>                         dev_err(&vdev->dev, "device MTU appears
to have changed "
>                                 "it is now %d < %d", mtu,
dev->min_mtu);
> -                       goto free_stats;
> +                       goto free_vf_stats;
>                 }
>
>                 dev->mtu = mtu;
> @@ -2692,7 +2789,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>         /* Allocate/initialize the rx/tx queues, and invoke find_vqs */
>         err = init_vqs(vi);
>         if (err)
> -               goto free_stats;
> +               goto free_vf_stats;
>
>  #ifdef CONFIG_SYSFS
>         if (vi->mergeable_rx_bufs)
> @@ -2747,6 +2844,8 @@ static int virtnet_probe(struct virtio_device *vdev)
>         cancel_delayed_work_sync(&vi->refill);
>         free_receive_page_frags(vi);
>         virtnet_del_vqs(vi);
> +free_vf_stats:
> +       free_percpu(vi->vf_stats);
>  free_stats:
>         free_percpu(vi->stats);
>  free:
> @@ -2768,19 +2867,184 @@ static void remove_vq_common(struct virtnet_info
*vi)
>         virtnet_del_vqs(vi);
>  }
>
> +static struct net_device *get_virtio_bymac(const u8 *mac)
> +{
> +       struct net_device *dev;
> +
> +       ASSERT_RTNL();
> +
> +       for_each_netdev(&init_net, dev) {
> +               if (dev->netdev_ops != &virtnet_netdev)
> +                       continue;       /* not a virtio_net device */
> +
> +               if (ether_addr_equal(mac, dev->perm_addr))
> +                       return dev;
> +       }
> +
> +       return NULL;
> +}
> +
> +static struct net_device *get_virtio_byref(struct net_device *vf_netdev)
> +{
> +       struct net_device *dev;
> +
> +       ASSERT_RTNL();
> +
> +       for_each_netdev(&init_net, dev) {
> +               struct virtnet_info *vi;
> +
> +               if (dev->netdev_ops != &virtnet_netdev)
> +                       continue;       /* not a virtio_net device */
> +
> +               vi = netdev_priv(dev);
> +               if (rtnl_dereference(vi->vf_netdev) == vf_netdev)
> +                       return dev;     /* a match */
> +       }
> +
> +       return NULL;
> +}
> +
> +/* Called when VF is injecting data into network stack.
> + * Change the associated network device from VF to virtio.
> + * note: already called with rcu_read_lock
> + */
> +static rx_handler_result_t virtnet_vf_handle_frame(struct sk_buff **pskb)
> +{
> +       struct sk_buff *skb = *pskb;
> +       struct net_device *ndev =
rcu_dereference(skb->dev->rx_handler_data);
> +       struct virtnet_info *vi = netdev_priv(ndev);
> +       struct virtnet_vf_pcpu_stats *pcpu_stats > +                    
this_cpu_ptr(vi->vf_stats);
> +
> +       skb->dev = ndev;
> +
> +       u64_stats_update_begin(&pcpu_stats->syncp);
> +       pcpu_stats->rx_packets++;
> +       pcpu_stats->rx_bytes += skb->len;
> +       u64_stats_update_end(&pcpu_stats->syncp);
> +
> +       return RX_HANDLER_ANOTHER;
> +}
> +
> +static int virtnet_vf_join(struct net_device *vf_netdev,
> +                          struct net_device *ndev)
> +{
> +       int ret;
> +
> +       ret = netdev_rx_handler_register(vf_netdev,
> +                                        virtnet_vf_handle_frame, ndev);
> +       if (ret != 0) {
> +               netdev_err(vf_netdev,
> +                          "can not register virtio VF receive handler
(err = %d)\n",
> +                          ret);
> +               goto rx_handler_failed;
> +       }
> +
> +       ret = netdev_upper_dev_link(vf_netdev, ndev, NULL);
> +       if (ret != 0) {
> +               netdev_err(vf_netdev,
> +                          "can not set master device %s (err =
%d)\n",
> +                          ndev->name, ret);
> +               goto upper_link_failed;
> +       }
> +
> +       vf_netdev->flags |= IFF_SLAVE;
> +
> +       /* Align MTU of VF with master */
> +       ret = dev_set_mtu(vf_netdev, ndev->mtu);
> +       if (ret)
> +               netdev_warn(vf_netdev,
> +                           "unable to change mtu to %u\n",
ndev->mtu);
> +
> +       call_netdevice_notifiers(NETDEV_JOIN, vf_netdev);
> +
> +       netdev_info(vf_netdev, "joined to %s\n", ndev->name);
> +       return 0;
> +
> +upper_link_failed:
> +       netdev_rx_handler_unregister(vf_netdev);
> +rx_handler_failed:
> +       return ret;
> +}
> +
> +static int virtnet_register_vf(struct net_device *vf_netdev)
> +{
> +       struct net_device *ndev;
> +       struct virtnet_info *vi;
> +
> +       if (vf_netdev->addr_len != ETH_ALEN)
> +               return NOTIFY_DONE;
> +
> +       /* We will use the MAC address to locate the virtio_net interface
to
> +        * associate with the VF interface. If we don't find a matching
> +        * virtio interface, move on.
> +        */
> +       ndev = get_virtio_bymac(vf_netdev->perm_addr);
> +       if (!ndev)
> +               return NOTIFY_DONE;
> +
> +       vi = netdev_priv(ndev);
> +       if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_BACKUP))
> +               return NOTIFY_DONE;
> +
> +       if (rtnl_dereference(vi->vf_netdev))
> +               return NOTIFY_DONE;
> +
> +       if (virtnet_vf_join(vf_netdev, ndev) != 0)
> +               return NOTIFY_DONE;
> +
> +       netdev_info(ndev, "VF registering %s\n",
vf_netdev->name);
> +
> +       dev_hold(vf_netdev);
> +       rcu_assign_pointer(vi->vf_netdev, vf_netdev);
> +
> +       return NOTIFY_OK;
> +}
> +
> +static int virtnet_unregister_vf(struct net_device *vf_netdev)
> +{
> +       struct net_device *ndev;
> +       struct virtnet_info *vi;
> +
> +       ndev = get_virtio_byref(vf_netdev);
> +       if (!ndev)
> +               return NOTIFY_DONE;
> +
> +       vi = netdev_priv(ndev);
> +       if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_BACKUP))
> +               return NOTIFY_DONE;
> +
> +       netdev_info(ndev, "VF unregistering %s\n",
vf_netdev->name);
> +
> +       netdev_rx_handler_unregister(vf_netdev);
> +       netdev_upper_dev_unlink(vf_netdev, ndev);
> +       RCU_INIT_POINTER(vi->vf_netdev, NULL);
> +       dev_put(vf_netdev);
> +
> +       return NOTIFY_OK;
> +}
> +
>  static void virtnet_remove(struct virtio_device *vdev)
>  {
>         struct virtnet_info *vi = vdev->priv;
> +       struct net_device *vf_netdev;
>
>         virtnet_cpu_notif_remove(vi);
>
>         /* Make sure no work handler is accessing the device. */
>         flush_work(&vi->config_work);
>
> +       rtnl_lock();
> +       vf_netdev = rtnl_dereference(vi->vf_netdev);
> +       if (vf_netdev)
> +               virtnet_unregister_vf(vf_netdev);
> +       rtnl_unlock();
> +
>         unregister_netdev(vi->dev);
>
>         remove_vq_common(vi);
>
> +       free_percpu(vi->vf_stats);
>         free_percpu(vi->stats);
>         free_netdev(vi->dev);
>  }
> @@ -2859,6 +3123,42 @@ static struct virtio_driver virtio_net_driver = {
>  #endif
>  };
>
> +static int virtio_netdev_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_netdev)
> +               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 VF */
> +       if (is_vlan_dev(event_dev))
> +               return NOTIFY_DONE;
> +
> +       /* Avoid Bonding master dev with same MAC registering as VF */
> +       if ((event_dev->priv_flags & IFF_BONDING) &&
> +           (event_dev->flags & IFF_MASTER))
> +               return NOTIFY_DONE;
> +
> +       switch (event) {
> +       case NETDEV_REGISTER:
> +               return virtnet_register_vf(event_dev);
> +       case NETDEV_UNREGISTER:
> +               return virtnet_unregister_vf(event_dev);
> +       default:
> +               return NOTIFY_DONE;
> +       }
> +}
> +
> +static struct notifier_block virtio_netdev_notifier = {
> +       .notifier_call = virtio_netdev_event,
> +};
> +
>  static __init int virtio_net_driver_init(void)
>  {
>         int ret;
> @@ -2877,6 +3177,8 @@ static __init int virtio_net_driver_init(void)
>          ret = register_virtio_driver(&virtio_net_driver);
>         if (ret)
>                 goto err_virtio;
> +
> +       register_netdevice_notifier(&virtio_netdev_notifier);
>         return 0;
>  err_virtio:
>         cpuhp_remove_multi_state(CPUHP_VIRT_NET_DEAD);
> @@ -2889,6 +3191,7 @@ module_init(virtio_net_driver_init);
>
>  static __exit void virtio_net_driver_exit(void)
>  {
> +       unregister_netdevice_notifier(&virtio_netdev_notifier);
>         unregister_virtio_driver(&virtio_net_driver);
>         cpuhp_remove_multi_state(CPUHP_VIRT_NET_DEAD);
>         cpuhp_remove_multi_state(virtionet_online);
> --
> 2.14.3
>

On 2018?01?12? 13:58, Sridhar Samudrala wrote:
>   static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device
*dev)
>   {
>   	struct virtnet_info *vi = netdev_priv(dev);
>   	int qnum = skb_get_queue_mapping(skb);
>   	struct send_queue *sq = &vi->sq[qnum];
> +	struct net_device *vf_netdev;
>   	int err;
>   	struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
>   	bool kick = !skb->xmit_more;
>   	bool use_napi = sq->napi.weight;
>   
> +	/* If VF is present and up then redirect packets
> +	 * called with rcu_read_lock_bh
> +	 */
> +	vf_netdev = rcu_dereference_bh(vi->vf_netdev);
> +	if (vf_netdev && netif_running(vf_netdev) &&
> +	    !netpoll_tx_running(dev) &&
> +	    is_unicast_ether_addr(eth_hdr(skb)->h_dest))
> +		return virtnet_vf_xmit(dev, vf_netdev, skb);
> +
A question here.

If I read the code correctly, all features were validated against virtio 
instead VF before transmitting. This assumes VF's feature is a superset 
of virtio, does this really work? Do we need to sanitize the feature 
before joining? (e.g at last NETIF_R_GSO_ROBUST needs to be removed).

Thanks

On Thu, Jan 11, 2018 at 09:58:39PM -0800, Sridhar Samudrala
wrote:
> @@ -2859,6 +3123,42 @@ static struct virtio_driver virtio_net_driver = {
>  #endif
>  };
>  
> +static int virtio_netdev_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_netdev)
> +		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 VF */
> +	if (is_vlan_dev(event_dev))
> +		return NOTIFY_DONE;
> +
> +	/* Avoid Bonding master dev with same MAC registering as VF */
> +	if ((event_dev->priv_flags & IFF_BONDING) &&
> +	    (event_dev->flags & IFF_MASTER))
> +		return NOTIFY_DONE;
> +
> +	switch (event) {
> +	case NETDEV_REGISTER:
> +		return virtnet_register_vf(event_dev);
> +	case NETDEV_UNREGISTER:
> +		return virtnet_unregister_vf(event_dev);
> +	default:
> +		return NOTIFY_DONE;
> +	}
> +}
> +
> +static struct notifier_block virtio_netdev_notifier = {
> +	.notifier_call = virtio_netdev_event,
> +};
> +
>  static __init int virtio_net_driver_init(void)
>  {
>  	int ret;
> @@ -2877,6 +3177,8 @@ static __init int virtio_net_driver_init(void)
>          ret = register_virtio_driver(&virtio_net_driver);
>  	if (ret)
>  		goto err_virtio;
> +
> +	register_netdevice_notifier(&virtio_netdev_notifier);
>  	return 0;
>  err_virtio:
>  	cpuhp_remove_multi_state(CPUHP_VIRT_NET_DEAD);
> @@ -2889,6 +3191,7 @@ module_init(virtio_net_driver_init);
>  
>  static __exit void virtio_net_driver_exit(void)
>  {
> +	unregister_netdevice_notifier(&virtio_netdev_notifier);
>  	unregister_virtio_driver(&virtio_net_driver);
>  	cpuhp_remove_multi_state(CPUHP_VIRT_NET_DEAD);
>  	cpuhp_remove_multi_state(virtionet_online);
I have a question here: what if PT device driver module loads
and creates a device before virtio?

> -- 
> 2.14.3