Re: [virtio-dev] Re: [PATCH 0/5] virtio: introduce SUSPEND bit and vq state

Jason Wang
2023-09-21T03:26:32Z

On Wed, Sep 20, 2023 at 8:41 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Wed, Sep 20, 2023 at 08:05:49AM -0400, Michael S. Tsirkin wrote:
> > On Wed, Sep 20, 2023 at 07:22:32PM +0800, Zhu, Lingshan wrote:
> > >
> > >
> > > On 9/20/2023 6:36 PM, Michael S. Tsirkin wrote:
> > > > On Wed, Sep 20, 2023 at 02:06:13PM +0800, Zhu, Lingshan wrote:
> > > > >
> > > > > On 9/19/2023 2:49 AM, Michael S. Tsirkin wrote:
> > > > > > On Mon, Sep 18, 2023 at 06:41:55PM +0000, Parav Pandit wrote:
> > > > > > > > Please refer to the code for setting FEATURES_OK.
> > > > > > > It wont work when one needs to suspend the device.
> > > > > > > There is no point of doing such work over registers as fundamental framework is over the AQ.
> > > > > > Well not really. It's over admin commands. When these were built the
> > > > > > intent always was that it's possible to use admin commands through
> > > > > > another interface, other than admin queue. Is there a problem
> > > > > > implementing admin commands over a memory BAR? For example, I can see
> > > > > > an "admin command" capability pointing at a BAR where
> > > > > > commands are supplied, and using a new group type referring to
> > > > > > device itself.
> > > > > I am not sure, if a bar cap would be implemented as a proxy for the admin vq
> > > > > based live migration.
> > > > Not a proxy for a vq in that there's no vq then.
> > > I think if the driver sends admin commands through a VF's bar, then
> > > VF forwards the admin commands to the PF, it acts like a proxy,
> > > or an agent. Anyway it takes admin commands.
> >
> > Why send them to the PF? They are controlling the VF anyway.
> >
> > > So the problems we have discussed still exist.
> > > >
> > > > > then the problems of admin vq LM that we have
> > > > > discussed
> > > > > still exist.
> > > > I freely admit the finer points of this extended flamewar have been lost
> > > > on me, and I wager I'm not the only one. I thought you wanted to migrate
> > > > the device just by accessing the device itself (e.g. the VF) without
> > > > accessing other devices (e.g. the PF), while Parav wants it in a
> > > > separate device so the whole of the device itself can passed through to
> > > > guest. Isn't this, fundamentally, the issue?
> > > we are implementing basic facilities for live migration.
> > >
> > > We have pointed out lots of issues, there are many discussions with
> > > Jason and Parav about the problems in migration by admin vq, for example:
> > > security, QOS and nested.
> >
> > /me shrugs
> > Thanks for the summary I guess. Same applies to almost any proposal.
> > What would help make progress is an explanation why this has grown into
> > a megathread. Do you understand Parav's thoughts well enough to
> > summarize them?
>
>
> And Parav same goes for you - can you summarize Zhu Lingshan's position?

The root cause for the long debate is that there are a lot of
misunderstandings between each other. This can be seen from Parav's
reply.

My understanding is it might be better that each side do a summary of
the both proposals.

Thanks