RE: [PATCH linux-next v3 0/6] vdpa: enable user to set mac, mtu

[Parav Pandit via Virtualization <virtualization@lists.linux-foundation.org>]

> From: Eli Cohen <elic@nvidia.com>
> Sent: Monday, August 9, 2021 10:51 AM
> 
> On Mon, Aug 09, 2021 at 11:07:50AM +0800, Jason Wang wrote:
> >
> > 在 2021/8/6 下午4:55, Parav Pandit 写道:
> > >
> > > > From: Michael S. Tsirkin <mst@redhat.com>
> > > > Sent: Friday, August 6, 2021 2:12 PM
> > >
> > > > >   enum vdpa_attr {
> > > > > @@ -33,6 +34,16 @@ enum vdpa_attr {
> > > > >   	VDPA_ATTR_DEV_MAX_VQS,			/* u32 */
> > > > >   	VDPA_ATTR_DEV_MAX_VQ_SIZE,		/* u16 */
> > > > > +	VDPA_ATTR_DEV_NET_CFG_MACADDR,		/*
> binary */
> > > > > +	VDPA_ATTR_DEV_NET_STATUS,		/* u8 */
> > > > > +	VDPA_ATTR_DEV_NET_CFG_MAX_VQP,		/*
> u16 */
> > > > > +	VDPA_ATTR_DEV_NET_CFG_MTU,		/* u16 */
> > > > > +	VDPA_ATTR_DEV_NET_CFG_SPEED,		/* u16 */
> > > > > +	VDPA_ATTR_DEV_NET_CFG_DUPLEX,		/* u16 */
> > > > > +	VDPA_ATTR_DEV_NET_CFG_RSS_MAX_KEY_LEN,	/* u8
> */
> > > > > +	VDPA_ATTR_DEV_NET_CFG_RSS_MAX_IT_LEN,	/*
> u16 */
> > > > > +	VDPA_ATTR_DEV_NET_CFG_RSS_HASH_TYPES,	/*
> u32 */
> > > > > +
> > > > >   	/* new attributes must be added above here */
> > > > >   	VDPA_ATTR_MAX,
> > > > >   };
> > > > The point is to try and not reinvent a dedicated vpda interface
> > > > where a generic one exits.
> > > > E.g. for phy things such as mac speed etc, I think most people are
> > > > using ethtool things right?
> > > As you know vdpa is the backend device for the front-end netdevice
> accessed by the ethtool.
> > > vdpa management tool here is composing the vdpa device.
> > >
> > > For example creator (hypervisor) of the vdpa devices knows that a
> > > guest VM is given 4 vcpus, So hypervisor creates a vdpa devices with
> > > config space layout as, max_virtqueue_pairs = 4.
> > > And the MAC address chosen by hypervisor in mac[6].
> > >
> > > Guest VM ethtool can still chose to use less number of channels.
> > >
> > > Typically,
> > > ethtool is for guest VM.
> > > vdpa device is in hypevisor.
> > >
> > > How can hypervisor compose a vdpa device without any tool?
> > > How can it tell ethtool, what is supported and what are the defaults?
> >
> >
> > Reread the cover letter:
> >
> > "
> >
> > This patchset enables users to set the mac address and mtu of the vdpa
> > device once the device is created.
> >
> > "
> >
> > It looks to me the mechanism that introduced in the series is not for
> > provisioning but for post-creation configuration?
> >
> 
> The difference is subtle. In both cases you provide configuration.
> 
> 
> >
> > >
> > > I must be misunderstanding your comment about ethtool.
> > > Can you please explain?
> >
> >
> > I guess the meaning is that, if the vDPA is assigned to guest, it's
> > the charge of guest to configure the MTU/MAC/RSS via the existing
> > management interface like ethtool/iproute2 netlink protocol. The
> > control virtqueue is designed for this.
> >
> 
> I was under the impression that we want somehow to control the capablity if
> the guest to use arbitrary MAC addresses.
> If this is is not required than I think control VQ is the mechanism to use.
How does the guest VM identify which unique mac address to set on this virtio net device when this is the only device in the VM?
Usually hypervisor knows what mac to set for a VM.

How do you set up the config space of the vdpa device migrating from source to destination hypervisor?
Is this done through qemu vhost framework to setup the config space?
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