On Mon, 2023-01-09 at 18:54 +0000, Dr. David Alan Gilbert wrote: > * James Bottomley (j...@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 (j...@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?
The backend driver contains state checks to prevent this, so if you follow the standard migration in https://www.qemu.org/docs/master/devel/migration.html it detects that you have done a migration on shutdown and simply closes the TPM socket. On start up it sees you're in migrate and doesn't do the power on reset of the TPM. James
