Re: [PATCH net-next v9 3/4] virtio_net: Extend virtio to use VF datapath when available

["Samudrala, Sridhar" <sridhar.samudrala@intel.com>]

On 4/28/2018 1:24 AM, Jiri Pirko wrote:
> Fri, Apr 27, 2018 at 07:06:59PM CEST, sridhar.samudrala@intel.com wrote:
> > This patch enables virtio_net to switch over to a VF datapath when a VF
> > netdev is present with the same MAC address. It allows live migration
> > of a VM with a direct attached VF without the need to setup a bond/team
> > between a VF and virtio net device in the guest.
> >
> > The hypervisor needs to enable only one datapath at any time so that
> > packets don't get looped back to the VM over the other datapath. When a VF
> Why? Both datapaths could be enabled at a time. Why the loop on
> hypervisor side would be a problem. This in not an issue for
> bonding/team as well.

Somehow the hypervisor needs to make sure that the broadcasts/multicasts from the VM
sent over the VF datapath don't get looped back to the VM via the virtio-net datapth.
This can happen if both datapaths are enabled at the same time.

I would think this is an issue even with bonding/team as well when virtio-net and
VF are backed by the same PF.


> > is plugged, the virtio datapath link state can be marked as down. The
> > hypervisor needs to unplug the VF device from the guest on the source host
> > and reset the MAC filter of the VF to initiate failover of datapath to
> "reset the MAC filter of the VF" - you mean "set the VF mac"?

Yes.  the PF should take away the MAC address assigned to the VF so that the PF
starts receiving those packets.

> > virtio before starting the migration. After the migration is completed,
> > the destination hypervisor sets the MAC filter on the VF and plugs it back
> > to the guest to switch over to VF datapath.
> >
> > It uses the generic failover framework that provides 2 functions to create
> > and destroy a master failover netdev. When STANDBY feature is enabled, an
> > additional netdev(failover netdev) is created that acts as a master device
> > and tracks the state of the 2 lower netdevs. The original virtio_net netdev
> > is marked as 'standby' netdev and a passthru device with the same MAC is
> > registered as 'primary' netdev.
> >
> > This patch is based on the discussion initiated by Jesse on this thread.
> > https://marc.info/?l=linux-virtualization&m=151189725224231&w=2
> [...]