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

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

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.

> Adding device state save/load does not change anything here.

It's as good a time as any to try to standardize things and
not just let each driver do whatever it wants. In particular
if you consider things like cross version support it's
a hard problem where vendors are sure to get it wrong without
guidance.

-- 
MST