Re: [PATCH v2 1/1] virtio_net: notify MAC address change on device initialization
From: Laurent Vivier
Date: Fri Jan 27 2023 - 07:29:33 EST
On 1/27/23 12:08, Michael S. Tsirkin wrote:
On Tue, Jan 24, 2023 at 12:04:24PM +0100, Laurent Vivier wrote:
On 1/24/23 11:15, Michael S. Tsirkin wrote:
On Mon, Jan 23, 2023 at 01:00:22PM +0100, Laurent Vivier wrote:
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.
And then what exactly happens? Does hardware drop the outgoing
or the incoming packets? Pls include in the commit log.
I don't know. There is nothing in the kernel logs.
The ping error is: "Destination Host Unreachable"
I found the problem with the mlx5 driver as in "it doesn't work when MAC
address is not set"...
Perhaps Eli can explain what happens when the MAC address is not set?
Signed-off-by: Laurent Vivier <lvivier@xxxxxxxxxx>
---
drivers/net/virtio_net.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7723b2a49d8e..4bdc8286678b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3800,6 +3800,8 @@ 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 */
@@ -3956,6 +3958,18 @@ static int virtnet_probe(struct virtio_device *vdev)
pr_debug("virtnet: registered device %s with %d RX and TX vq's\n",
dev->name, max_queue_pairs);
+ /* a random MAC address has been assigned, notify the device */
+ if (!virtio_has_feature(vdev, VIRTIO_NET_F_MAC) &&
+ virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_MAC_ADDR)) {
Maybe add a comment explaining that we don't fail probe if
VIRTIO_NET_F_CTRL_MAC_ADDR is not there because
many devices work fine without getting MAC explicitly.
OK
+ 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)) {
+ dev_warn(&vdev->dev, "Failed to update MAC address.\n");
Here, I'm not sure we want to proceed. Is it useful sometimes?
I think reporting an error is always useful, but I can remove that if you prefer.
No the question was whether we should fail probe not
whether we print the warning.
Good question.
After all, as VIRTIO_NET_F_CTRL_MAC_ADDR is set, if VIRTIO_NET_CTRL_MAC_ADDR_SET fails it
means there is a real problem, so yes, we should fail.
I note that we deny with virtnet_set_mac_address.
+ }
+ }
+
return 0;
Also, some code duplication with virtnet_set_mac_address here.
Also:
When using the legacy interface, \field{mac} is driver-writable
which provided a way for drivers to update the MAC without
negotiating VIRTIO_NET_F_CTRL_MAC_ADDR.
How about factoring out code in virtnet_set_mac_address
and reusing that?
In fact, we can write in the field only if we have VIRTIO_NET_F_MAC
(according to virtnet_set_mac_address(), and this code is executed only if
we do not have VIRTIO_NET_F_MAC. So I think it's better not factoring the
code as we have only the control queue case to manage.
This will also handle corner cases such as VIRTIO_NET_F_STANDBY
which are not currently addressed.
F_STANDBY is only enabled when virtio-net device MAC address is equal to the
VFIO device MAC address, I don't think it can be enabled when the MAC
address is randomly assigned (in this case it has already failed in
net_failover_create(), as it has been called using the random mac address),
it's why I didn't check for it.
But the spec did not say there's a dependency :(.
My point is what should we do if there's F_STANDBY but no MAC?
Maybe add a separate patch clearing F_STANDBY in this case?
The simplest would be to add at the beginning of the probe function:
if (!virtio_has_feature(vdev, VIRTIO_NET_F_MAC) &&
virtio_has_feature(vdev, VIRTIO_NET_F_STANDBY)) {
pr_err("virtio-net: a standby device cannot be used without a MAC address");
return -EOPNOTSUPP;
}
And I think it would help a lot to debug misconfiguration of the interface.
Thanks,
Laurent
free_unregister_netdev:
--
2.39.0
Thanks,
Laurent