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

["Michael S. Tsirkin" <mst@redhat.com>]

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 bar is only a proxy, doesn't fix anything. and even larger
> > > > side channel attacking surface: vf-->pf-->vf
> > > In this model there's no pf. BAR belongs to vf itself
> > > and you submit commands for the VF through its BAR.
> > > Just separate from the pci config space.
> > If using the bar to process admin commands,
> > is this solution too heavy compared to my proposal in this series?
> 
> somewhat - because it's more comprehensive - you can actually
> migrate a device using it.
> this series just begins to define how to poke at some
> of the vq state - it's a subset of the necessary functionality.
> 
> And it will give you a bunch of side benefits, such as
> support for legacy compat commands that were merged.
> 
> 
> 
> > > 
> > > The whole attacking surface discussion is also puzzling.  We either are
> > > or are not discussing confidential computing/TDI.  I couldn't figure
> > > it out. This needs a separate thread I think.
> > I agree confidential computing is out of spec. Parva mentioned TDISP and
> > even
> > in TDISP spec, it explicitly defined some attacking model, and PF is an
> > example.
> > 
> > It is out of spec anyway.
> 
> OK so we are ignoring TDISP applications for now? Everyone agrees on
> that?
> 
> -- 
> MST