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Subject: Re: [PATCH] vdpa/mlx5: Use random MAC for the vdpa net instance
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Cindy Lu <lulu@redhat.com>, Eli Cohen <elic@nvidia.com>,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <128487fe-8736-6d9e-3d07-b55dcb92c9b0@redhat.com>
Date:   Wed, 2 Dec 2020 20:56:37 +0800
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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@redhat.com> 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@redhat.com> 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@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?
>>>>>>>>
>>>>>>> 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@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)?
>>>>>>> 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