Re: Live migration and PV device handling

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Fri, Apr 3, 2020 at 6:44 AM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> On 03/04/2020 13:32, Anastassios Nanos wrote:
> > Hi all,
> >
> > I am trying to understand how live-migration happens in xen. I am
> > looking in the HVM guest case and I have dug into the relevant parts
> > of the toolstack and the hypervisor regarding memory, vCPU context
> > etc.
> >
> > In particular, I am interested in how PV device migration happens. I
> > assume that the guest is not aware of any suspend/resume operations
> > being done
>
> Sadly, this assumption is not correct.  HVM guests with PV drivers
> currently have to be aware in exactly the same way as PV guests.
>
> Work is in progress to try and address this.  See
> https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=775a02452ddf3a6889690de90b1a94eb29c3c732
> (sorry - for some reason that doc isn't being rendered properly in
> https://xenbits.xen.org/docs/ )

That proposal is very interesting - first time it came across my radar
- but I dislike the idea that domain IDs need to be preserved for
uncooperative migration to work. Ideally I would be able to take
advantage of the same plumbing to perform forking of VMs with PV
drivers where preserving the domain id is impossible since its still
in use.

Tamas