Re: [virtio-comment] [PATCH V2 2/2] virtio: introduce STOP status bit

[Jason Wang <jasowang@redhat.com>]

å 2021/7/15 äå12:22, Max Gurtovoy åé:
> On 7/14/2021 6:07 PM, Stefan Hajnoczi wrote:
> > > It requires much more works than the simple virtqueue interface: 
> > > (the main
> > > issues is that the function is not self-contained in a single function)
> > >
> > > 1) how to interact with the existing device status state machine?
> > > 2) how to make it work in a nested environment?
> > > 3) how to migrate the PF?
> > > 4) do we need to allow more control other than just stop/freeze the 
> > > device
> > > in the admin virtqueue? If yes, how to handle the concurrent access 
> > > from PF
> > > and VF?
> > > 5) how it is expected to work with non-PCI virtio device?
> > I guess your device splitting proposal addresses some of these things?
> >
> > Max probably has the most to say about these points.
> >
> > If you want more input I can try to answer too, but I personally am not
> > developing devices that need this right now, so I might not be the best
> > person to propose solutions.
>
> I think we mentioned this in the past and agreed that the only common 
> entity between my solution for virtio VF migration to this proposal is 
> the new admin control queue.
>
> I can prepare some draft for this.
>
> In our solution the PF will manage migration process for it's VFs 
> using the PF admin queue. PF is not migratable.


That limits the use cases.


> I don't know who is using nested environments in production so don't 
> know if it worth talking about that.


There should be plenty users for the nested case.


> But, if you would like to implement it for testing, no problem. The VF 
> in level n, probably seen as PF in level n+1. So it can manage the 
> migration process for its nested VFs.


The PF dependency makes the design almost impossible to be used in a 
nested environment.


> For question 5) what non-PCI devices are interesting in live migration ?

Why not? Virtio support transport other than PCI (CCW, MMIO).

Thanks