Re: [PATCH 2/2] tpm: add backend for mssim

[Dr. David Alan Gilbert]

* James Bottomley (jejb@linux.ibm.com) wrote:
> On Mon, 2023-01-09 at 13:34 -0500, Stefan Berger wrote:
> > 
> > 
> > On 1/9/23 12:55, James Bottomley wrote:
> > > On Mon, 2023-01-09 at 17:52 +0000, Dr. David Alan Gilbert wrote:
> > > > * James Bottomley (jejb@linux.ibm.com) wrote:
> > > [...]
> > > > > external MSSIM TPM emulator has to be kept running to preserve
> > > > > the state.  If you restart it, the migration will fail.
> > > > 
> > > > Document that and we're getting there.
> > > 
> > > 
> > > The documentation in the current patch series says
> > > 
> > > ----
> > > The mssim backend supports snapshotting and migration, but the
> > > state of the Microsoft Simulator server must be preserved (or the
> > > server kept running) outside of QEMU for restore to be successful.
> > > ----
> > > 
> > > What, beyond this would you want to see?
> > 
> > mssim today lacks the functionality of marshalling and unmarshalling
> > the permanent and volatile state of the TPM 2, which are both needed
> > for snapshot support. How does this work with mssim?
> 
> You preserve the state by keeping the simulator running as the above
> says.  As long as you can preserve the state, there's no maximum time
> between snapshots.  There's no need of marshal/unmarshal if you do
> this.

So I think I can understand how that works with a suspend/resume; I'm
less sure about a live migration.

In a live migration, you normally start up the destination VM
qemu process and other processes attached to it, prior to the inwards
live migration of state.  Then you live migrate the state, then kill the
source.

With this mssim setup, will the start up of the destination attempt
to change the vtpm state during the initialisation?

Dave

> James
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK