Re: [PATCH] vdpa/mlx5: Use random MAC for the vdpa net instance

[Eli Cohen]

On Wed, Dec 02, 2020 at 04:23:11AM -0500, Michael S. Tsirkin wrote:
> On Wed, Dec 02, 2020 at 07:57:14AM +0200, Eli Cohen 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:
> > 
> > Thinking it over, at least in mlx5, I should always advertise
> > VIRTIO_NET_F_MAC and set a non zero MAC value. The source of the MAC can
> > be either randomly generated value by mlx5_vdpa or by a management tool.
> > This is important becauase we should not let the VM modify the MAC. If
> > we do it can set a MAC value identical to the mlx5 NIC driver and can
> > kidnap traffic that was not destined to it.
> > 
> > In addition, when VIRTIO_NET_F_MAC is published, attempts to change the
> > MAC address from the VM should result in error.
> 
> That is not what the spec says though.
> VIRTIO_NET_F_MAC only says whether mac is valid in the config space.
> Whether guest can control that depends on VIRTIO_NET_F_CTRL_MAC_ADDR:
> 
> 	The VIRTIO_NET_CTRL_MAC_ADDR_SET command is used to set the default MAC address which rx
> 	filtering accepts (and if VIRTIO_NET_F_MAC_ADDR has been negotiated, this will be reflected in mac in
> 	config space).
> 	The command-specific-data for VIRTIO_NET_CTRL_MAC_ADDR_SET is the 6-byte MAC address.

Two questions here:
1. Now we don't have support for control virtqueue. Yet, we must filter
packets based on MAC, what do you suggest to do here?

2. When control virtqueue is implemented, which admin entity is allowed
to change the MAC filtering table?

> 
> 
> 
> 
> > 
> > > 
> > > 1) get a random mac
> > > 2) advertise VIRTIO_NET_F_MAC
> > > 3) set the random mac to vDPA through set_config
> > > 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
> > > 
>