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Subject: Re: [PATCH] vdpa/mlx5: Use random MAC for the vdpa net instance
To:     "Michael S. Tsirkin" <mst@redhat.com>, Eli Cohen <elic@nvidia.com>
Cc:     Cindy Lu <lulu@redhat.com>,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <13d33e2c-ea99-6625-83fd-6cb223dd103b@redhat.com>
Date:   Wed, 2 Dec 2020 21:00:07 +0800
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On 2020/12/2 下午8:17, Michael S. Tsirkin wrote:
> On Wed, Dec 02, 2020 at 02:12:41PM +0200, Eli Cohen wrote:
>> 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@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:
>>>> 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?
> How about an ioctl to pass the mac to the device?
> Maybe mirroring the control vq struct format ...


I think we'd better avoid such ad-hoc ioctls to make vhost-vDPA type 
independent. And doing this means we need to seek another way for 
virtio-vdpa drivers.

Thanks


>
>> 2. When control virtqueue is implemented, which admin entity is allowed
>> to change the MAC filtering table?
> It's up to the hypervisor: if VIRTIO_NET_F_CTRL_MAC_ADDR
> is enabled this means hypervisor trusts the guest with full
> access to NIC network.
> If it's clear then mac must be set by hardware or the hypervisor.
>