Re: [Qemu-devel] TPM status

[Javier Martinez Canillas]

On 06/29/2017 06:09 PM, Stefan Berger wrote:
> On 06/29/2017 08:39 AM, Javier Martinez Canillas wrote:

[snip]

>>
>>> = TPM backend devices =
>>>
>>> The TPM implementation is split into two parts. The one part is the hardware
>>> interface, such as the TPM TIS interface described earlier, and the TPM 
>>> backend
>>> interface. The backend interfaces implement the interaction with a TPM 
>>> device,
>>> which may be a physical or an emulated device. The split between the front-
>>> and backend devices allows a frontend to be connected with any available
>>> backend. This enables the TIS interface to be used with the passthrough 
>>> backend
>>> or the (future) swtpm backend.
>> So we will need another TPM interface that implements the CRB interface? I
> 
> No. How did you infer that ?
> 

I thought that if the host firmware set the TPM2 Start Method to CRB instead of
TIS1.2+cancel, then the guest would have to use the same interface.

But now with your patch libvirt doesn't complain anymore about a missing cancel
sysfs file and I could access the host TPM2.0 as a pass-through device, even
when the host is using the tpm_crb driver while the guest uses the tpm_tis one.

Sorry for the confusion, I'm just been learning about the TPM and still trying
to make sense of all the different specifications and documents.

Best regards,
-- 
Javier Martinez Canillas
Software Engineer - Desktop Hardware Enablement
Red Hat