Re: [RFC PATCH 00/13] Add support for Mirror VM.

[James Bottomley <jejb@linux.ibm.com>]

On Tue, 2021-08-17 at 16:10 -0700, Steve Rutherford wrote:
> On Tue, Aug 17, 2021 at 3:57 PM James Bottomley <jejb@linux.ibm.com>
> wrote:
> > Realistically, migration is becoming a royal pain, not just for
> > confidential computing, but for virtual functions in general.  I
> > really think we should look at S3 suspend, where we shut down the
> > drivers and then reattach on S3 resume as the potential pathway to
> > getting migration working both for virtual functions and this use
> > case.
> 
> This type of migration seems a little bit less "live", which makes me
> concerned about its performance characteristics.

Well, there are too many scenarios we just fail at migration today.  We
need help from the guest to quiesce or shut down the interior devices,
and S3 suspend seems to be the machine signal for that.  I think in
most clouds guests would accept some loss of "liveness" for a gain in
reliability as long as we keep them within the SLA ... which is 5
minutes a year for 5 nines.  Most failed migrations also instantly fail
SLAs because of the recovery times involved so I don't see what's to be
achieved by keeping the current "we can migrate sometimes" approach.

James