On Mon, Apr 03, 2023 at 08:27:28PM +0000, Parav Pandit wrote:
> 
> > From: Stefan Hajnoczi <stefanha@redhat.com>
> > Sent: Monday, April 3, 2023 3:10 PM
> 
> 
> > Maybe call it "Memory-mapped Transitional"? That name would be easier to
> > understand.
> >
> Sounds fine to me.
>  
> > > > Modern devices were added to Linux in 2014 and support SR-IOV.
> > >
> > > > Why is it
> > > > important to support Transitional (which really means Legacy
> > > > devices, otherwise Modern devices would be sufficient)?
> > > >
> > > To support guest VMs which only understand legacy devices and
> > > unfortunately they are still in much wider use by the users.
> > 
> > I wonder which guest software without Modern VIRTIO support will still be
> > supported by the time Transitional MMR software and hardware becomes
> > available. Are you aiming for particular guest software versions?
> 
> Transitional MMR hardware is available almost now.
> Transitional MMR software is also WIP to be available as soon as we ratify the spec via tvq or via mmr or both.
> This will be support the guest sw version such as 2.6.32.754 kernel.

That is a RHEL 6 kernel. RHEL 6 entered Extended Life Cycle Support on
November 30, 2020 (https://access.redhat.com/articles/4665701).

I would use existing software emulation for really old guests, but if
you see an opportunity for hardware passthrough, then why not.

Stefan