RE: [Xen-devel] Re: Getting rid of xenbus_suspend(): tpmfront driverimpacted?

[Stefan Berger <stefanb@xxxxxxxxxx>]

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx wrote on 11/05/2006
11:44:14 AM:

> The TPM protocol in contrast assumes a
> > reliable connection from the computer to the device and that
all
> commands
> > finish correctly and responses are received by the apps *and*
that
> requests
> > are not resent. How does the block driver handle this? Will the
> frontend
> > driver still receive explicit notification of a shutdown?
> 
> Blkfront remembers un-acknowledged requests and reissues them after
a
> re-connect. It doesn't matter whether the requests have previously
been

I  cannot possibly reissue commands like a TPM_Extend(value).
It's performing a hashing operation on a register of the TPM using a formular
like

PCR_n = SHA1(PCR_n || value)

where || is a concatenation of two byte arrays. 

So issuing this command twice would put the TPM's
PCR register into a state that it is not supposed to be in.

> issued or not, as we know there will be no reordering hazards within
the
> request stream, as there are no ordering guarantees. It currently
> doesn't use the suspend notification.

Unfortunately the TPM is a device with different constraints.

  Stefan

PS: Specs for the TPM are here:
https://www.trustedcomputinggroup.org/specs/TPM/tpmwg-mainrev62_Part3_Commands.pdf
page 114 talks about the TPM_Extend command.


> 
> Ian
> 
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