Virtualization - Jan 2023 - [PATCH v3 2/2] virtio_net: notify MAC address change on device initialization

When the MAC address is not provided by the vdpa device virtio_net
driver assigns a random one without notifying the device.
The consequence, in the case of mlx5_vdpa, is the internal routing
tables of the device are not updated and this can block the
communication between two namespaces.

To fix this problem, use virtnet_send_command(VIRTIO_NET_CTRL_MAC)
to set the address from virtnet_probe() when the MAC address is
not provided by the device.

v3:
  - update comments
  - fail probe if VIRTIO_NET_CTRL_MAC_ADDR_SET fails
  - move the virtnet_send_command() upper, inside the RTNL lock,
    this simplifies the cleanup in case of error, and a future patch
    from Jason adds an ASSERT_RTNL() in virtnet_send_command()
    ("virtio-net: convert rx mode setting to use workqueue")
  - add a patch to disable F_STANDBY if F_MAC is not set

v2:
  - remove vdpa_sim related fixes
  - check virtio_has_feature(vdev, VIRTIO_NET_F_MAC) rather than
    addr_assign_type

Laurent Vivier (2):
  virtio_net: disable VIRTIO_NET_F_STANDBY if VIRTIO_NET_F_MAC is not
    set
  virtio_net: notify MAC address change on device initialization

 drivers/net/virtio_net.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

-- 
2.39.1

failover relies on the MAC address to pair the primary and the standby
devices:

  "[...] the hypervisor needs to enable VIRTIO_NET_F_STANDBY
   feature on the virtio-net interface and assign the same MAC address
   to both virtio-net and VF interfaces."

  Documentation/networking/net_failover.rst

This patch disables the STANDBY feature if the MAC address is not
provided by the hypervisor.

Signed-off-by: Laurent Vivier <lvivier at redhat.com>
---
 drivers/net/virtio_net.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7723b2a49d8e..7d700f8e545a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3688,6 +3688,12 @@ static int virtnet_validate(struct virtio_device *vdev)
 			__virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
 	}
 
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_STANDBY) &&
+	    !virtio_has_feature(vdev, VIRTIO_NET_F_MAC)) {
+		dev_warn(&vdev->dev, "device advertises feature
VIRTIO_NET_F_STANDBY but not VIRTIO_NET_F_MAC, disabling standby");
+		__virtio_clear_bit(vdev, VIRTIO_NET_F_STANDBY);
+	}
+
 	return 0;
 }
 
-- 
2.39.1

In virtnet_probe(), if the device doesn't provide a MAC address the
driver assigns a random one.
As we modify the MAC address we need to notify the device to allow it
to update all the related information.

The problem can be seen with vDPA and mlx5_vdpa driver as it doesn't
assign a MAC address by default. The virtio_net device uses a random
MAC address (we can see it with "ip link"), but we can't ping a
net
namespace from another one using the virtio-vdpa device because the
new MAC address has not been provided to the hardware:
RX packets are dropped since they don't go through the receive filters,
TX packets go through unaffected.

Signed-off-by: Laurent Vivier <lvivier at redhat.com>
---
 drivers/net/virtio_net.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7d700f8e545a..704a05f1c279 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3806,6 +3806,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 		eth_hw_addr_set(dev, addr);
 	} else {
 		eth_hw_addr_random(dev);
+		dev_info(&vdev->dev, "Assigned random MAC address %pM\n",
+			 dev->dev_addr);
 	}
 
 	/* Set up our device-specific information */
@@ -3933,6 +3935,24 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 	virtio_device_ready(vdev);
 
+	/* a random MAC address has been assigned, notify the device.
+	 * We don't fail probe if VIRTIO_NET_F_CTRL_MAC_ADDR is not there
+	 * because many devices work fine without getting MAC explicitly
+	 */
+	if (!virtio_has_feature(vdev, VIRTIO_NET_F_MAC) &&
+	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_MAC_ADDR)) {
+		struct scatterlist sg;
+
+		sg_init_one(&sg, dev->dev_addr, dev->addr_len);
+		if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_MAC,
+					  VIRTIO_NET_CTRL_MAC_ADDR_SET, &sg)) {
+			pr_debug("virtio_net: setting MAC address failed\n");
+			rtnl_unlock();
+			err = -EINVAL;
+			goto free_unregister_netdev;
+		}
+	}
+
 	rtnl_unlock();
 
 	err = virtnet_cpu_notif_add(vi);
-- 
2.39.1