Re: [PATCH] vdpa/mlx5: Use random MAC for the vdpa net instance
From: Jason Wang
Date: Wed Dec 02 2020 - 07:58:22 EST
On 2020/12/2 下午5:30, Michael S. Tsirkin wrote:
On Wed, Dec 02, 2020 at 12:18:36PM +0800, Jason Wang wrote:
On 2020/12/1 下午5:23, Cindy Lu wrote:
On Mon, Nov 30, 2020 at 11:33 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
On Mon, Nov 30, 2020 at 06:41:45PM +0800, Cindy Lu wrote:
On Mon, Nov 30, 2020 at 5:33 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
On Mon, Nov 30, 2020 at 11:27:59AM +0200, Eli Cohen wrote:
On Mon, Nov 30, 2020 at 04:00:51AM -0500, Michael S. Tsirkin wrote:
On Mon, Nov 30, 2020 at 08:27:46AM +0200, Eli Cohen wrote:
On Sun, Nov 29, 2020 at 03:08:22PM -0500, Michael S. Tsirkin wrote:
On Sun, Nov 29, 2020 at 08:43:51AM +0200, Eli Cohen wrote:
We should not try to use the VF MAC address as that is used by the
regular (e.g. mlx5_core) NIC implementation. Instead, use a random
generated MAC address.
Suggested by: Cindy Lu <lulu@xxxxxxxxxx>
Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
I didn't realise it's possible to use VF in two ways
with and without vdpa.
Using a VF you can create quite a few resources, e.g. send queues
recieve queues, virtio_net queues etc. So you can possibly create
several instances of vdpa net devices and nic net devices.
Could you include a bit more description on the failure
mode?
Well, using the MAC address of the nic vport is wrong since that is the
MAC of the regular NIC implementation of mlx5_core.
Right but ATM it doesn't coexist with vdpa so what's the problem?
This call is wrong: mlx5_query_nic_vport_mac_address()
Is switching to a random mac for such an unusual
configuration really justified?
Since I can't use the NIC's MAC address, I have two options:
1. To get the MAC address as was chosen by the user administering the
NIC. This should invoke the set_config callback. Unfortunately this
is not implemented yet.
2. Use a random MAC address. This is OK since if (1) is implemented it
can always override this random configuration.
It looks like changing a MAC could break some guests,
can it not?
No, it will not. The current version of mlx5 VDPA does not allow regular
NIC driver and VDPA to co-exist. I have patches ready that enable that
from steering point of view. I will post them here once other patches on
which they depend will be merged.
https://patchwork.ozlabs.org/project/netdev/patch/20201120230339.651609-12-saeedm@xxxxxxxxxx/
Could you be more explicit on the following points:
- which configuration is broken ATM (as in, two device have identical
macs? any other issues)?
The only wrong thing is the call to mlx5_query_nic_vport_mac_address().
It's not breaking anything yet is wrong. The random MAC address setting
is required for the steering patches.
Okay so I'm not sure the Fixes tag at least is appropriate if it's a
dependency of a new feature.
- why won't device MAC change from guest point of view?
It's lack of implementation in qemu as far as I know.
Sorry not sure I understand. What's not implemented in QEMU?
HI Michael, there are some bug in qemu to set_config, this will fix in future,
But this patch is still needed, because without this patch the mlx
driver will give an 0 mac address to qemu
and qemu will overwrite the default mac address. This will cause traffic down.
Hmm the patch description says VF mac address, not 0 address. Confused.
If there's no mac we can clear VIRTIO_NET_F_MAC and have guest
use a random value ...
I'm not sure this can work for all types of vDPA (e.g it could not be a
learning bridge in the swtich).
hi Michael，
I have tried as your suggestion, seems even remove the
VIRTIO_NET_F_MAC the qemu will still call get_cinfig and overwrite the
default address in VM,
This looks a bug in qemu, in guest driver we had:
/* Configuration may specify what MAC to use. Otherwise random. */
if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
virtio_cread_bytes(vdev,
offsetof(struct virtio_net_config, mac),
dev->dev_addr, dev->addr_len);
else
eth_hw_addr_random(dev);
this process is like
vdpa _init -->qemu call get_config ->mlx driver will give an mac
address with all 0-->
qemu will not check this mac address and use it --> overwrite the mac
address in qemu
So for my understanding there are several method to fix this problem
1, qemu check the mac address, if the mac address is all 0, qemu will
ignore it and set the random mac address to mlx driver.
So my understanding is that, if mac address is all 0, vDPA parent should not
advertise VIRTIO_NET_F_MAC. And qemu should emulate this feature as you did:
1) get a random mac
To me this looks like a spec violation.
If the driver negotiates the VIRTIO_NET_F_MAC feature, the driver MUST set
the physical address of the NIC to \field{mac}. Otherwise, it SHOULD
use a locally-administered MAC address (see \hyperref[intro:IEEE 802]{IEEE 802},
``9.2 48-bit universal LAN MAC addresses'').
One question here, what did "set" mean here consider the mac is given by
the device itself?
While not said explicitly, the assumption I think is that the local
MAC is not a local one.
2) advertise VIRTIO_NET_F_MAC
3) set the random mac to vDPA through set_config
that part looks wrong to me. Setting mac through set_config was
a pre-virtio-1.0 way to send mac to device. In 1.0 we have
VIRTIO_NET_CTRL_MAC_ADDR_SET for that:
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.
Looks like it doesn't prevent us from doing so. Otherwise this brings an
implicit dependency for control virtqueue if we want to support 1.0?
Thanks
4) advertise the random mac to emulated config to guest
2. mlx driver checks the mac address and if this mac is 0, return fail
to qemu, but this need to change the UAPI.
uAPI is probably fine since ioctl can fail. We can change the to allow the
set_config to fail but virito spec doesn't have a way to advertise the error
in this case. Anyway, the driver only risk itself for setting a wrong value,
so we're probably fine.
Thanks
3. mlx driver it shelf should get an correct mac address while it init.
4. add check in qemu get_config function , if there is not F_MAC Then
ignore the mac address from mlx driver
not sure which method is more suitable ?
Thanks
Cindy
---
drivers/vdpa/mlx5/net/mlx5_vnet.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index 1fa6fcac8299..80d06d958b8b 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -1955,10 +1955,7 @@ void *mlx5_vdpa_add_dev(struct mlx5_core_dev *mdev)
if (err)
goto err_mtu;
- err = mlx5_query_nic_vport_mac_address(mdev, 0, 0, config->mac);
- if (err)
- goto err_mtu;
-
+ eth_random_addr(config->mac);
mvdev->vdev.dma_dev = mdev->device;
err = mlx5_vdpa_alloc_resources(&ndev->mvdev);
if (err)
--
2.26.2