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    SubjectRe: [PATCH] vdpa/mlx5: Use random MAC for the vdpa net instance
    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@redhat.com>
    > > > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
    > > > Signed-off-by: Eli Cohen <elic@nvidia.com>
    > >
    > > 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?

    > > 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@nvidia.com/

    Could you be more explicit on the following points:
    - which configuration is broken ATM (as in, two device have identical
    macs? any other issues)?
    - why won't device MAC change from guest point of view?


    > > > ---
    > > > 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
    > >

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