Re: [PATCH v6 2/2] tpm: add backend for mssim

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

On Fri, 2023-09-22 at 09:27 -0400, Stefan Berger wrote:
> 
> On 9/22/23 09:02, Daniel P. Berrangé wrote:
> > On Fri, Sep 22, 2023 at 08:41:19AM -0400, Stefan Berger wrote:
> > > On 9/22/23 02:00, Markus Armbruster wrote:
> > > > Found this cleaning out old mail, sorry for missing it until
> > > > now!
> > > > 
> > > > I think we owe James a quick decision wether we're willing to
> > > > take the feature.  Stefan, thoughts?
> > > I thought we discusses it back then. Does it handle snapshotting
> > > and migration correctly?
> > To quote the patch itself:
> > 
> >    +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.
> 
> How does 'it' support snapshotting where the state of the TPM can be 
> completely different depending on the snapshot?

In the same way we support things like external disk devices across
snapshot and migration: it's up to the owner of the device to preserve
the state for the next resume. If you muck with the state (or connect
the wrong device) all bets are off.

>   I know what it took to support this feature with swtpm/libtpms but
> I don't see the equivalent here in this backend driver nor in the TCG
> reference code that the underlying TPM 2 simulator is based upon.
> 
> I do not want to stand in the way of it being merged but please 
> understand that I will also neither maintain nor fix bugs related to
> it nor its related underlying simulator -- with James being the
> maintainer of it, this should be clear. I have reason why I am saying
> this and they come from dealing with the upstream TPM 2 reference
> code.

I already said I'll support this, and added a Maintainers entry and a
specific exclusion from your TPM maintainer entry. I'm not sure what
additional assurances I can give?

James