Re: Out-of-Process Device Emulation session at KVM Forum 2020

[Stefan Hajnoczi]

On Mon, Nov 02, 2020 at 05:34:50AM -0500, Michael S. Tsirkin wrote:
> On Mon, Nov 02, 2020 at 10:27:54AM +0000, Stefan Hajnoczi wrote:
> > On Mon, Nov 02, 2020 at 11:00:12AM +0800, Jason Wang wrote:
> > > 
> > > On 2020/10/30 下午7:13, Stefan Hajnoczi wrote:
> > > > > I still don't get why it must be opaque.
> > > > If the device state format needs to be in the VMM then each device
> > > > needs explicit enablement in each VMM (QEMU, cloud-hypervisor, etc).
> > > > 
> > > > Let's invert the question: why does the VMM need to understand the
> > > > device state of a_passthrough_  device?
> > > 
> > > 
> > > It's not a 100% passthrough device if you want to support live migration.
> > > E.g the device state save and restore is not under the control of drivers 
> > > in
> > > the guest.
> > 
> > VFIO devices are already not pure passthrough (even without mdev) since
> > the PCI bus is emulated and device-specific quirks may be implemented.
> 
> So since it's not a pure passthrough anyway, let's try to
> introduce some standards even if we can not always enforce
> them.

Yes, I agree. I've sent a document called "VFIO Migration" in a separate
email thread that defines how to orchestrate migration with versioning.
Maybe we can discuss the details there and figure out which guidelines
and device state representations to standardize.

Stefan

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