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

On 4/30/2018 12:12 AM, Jiri Pirko wrote:
Mon, Apr 30, 2018 at 05:00:33AM CEST, sridhar.samudrala@intel.com wrote:
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.
Why? Please see below.

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.

I believe that the scenario is the same as on an ordinary nic/swich


       /     \
     eth0   eth1
      |       |
      |       |
      p1      p2



It is perfectly valid to p1 and p2 be up and "bridged" together. Bond
has to cope with loop-backed frames. "Failover driver" should too,
it's the same scenario.

OK. So looks like we should be able to handle this by returning RX_HANDLER_EXACT
for frames received on standby device when primary is present.

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