[PATCH v1 1/8] docs: documentation and schema for the new TPM Proxy device

[Stefan Berger]

On 5/8/20 8:06 AM, Daniel Henrique Barboza wrote:
> QEMU 4.1.0 introduced a new device type called TPM Proxy, currently
> implemented by PPC64 guests via a new virtual device called
> 'spapr-tpm-proxy' (see QEMU 0fb6bd073230 for more info).
>
> The TPM Proxy device interacts with a TPM Resource Manager, a host
> device capable of multiplexing the host TPM with multiple processes.
> This allows multiple guests to access some TPM features at the
> same time. Note that this mode of operation does not provide
> full TPM features to be available for the guest - for that case
> the guest still needs to assign a vTPM device (tpm-spapr for
> PPC64 guests). Although redundant, there is currently no technical
> limitation for a guest to assign both a vTPM and a TPM Proxy at the
> same time.
>
> This patch adds documentation and schema for the new TPM Proxy device.
> An example of a TPM Proxy device connected to a TPM Resource Manager
> '/dev/tpmrm0' will look like this:
>
>    <tpmproxy model='spapr-tpm-proxy'>
>      <device path='/dev/tpmrm0'/>
>    </tpmproxy>

We already have:

     <backend type='passthrough'>
       <device path='/dev/tpm0'/>
     </backend>

Now what is the difference between this tpm-proxy device using 
/dev/tpmrm0 and having the existing passthrough device use /dev/tpmrm0?  
Is there any useful filtering going on by the tpm-proxy device? If not, 
why not use passthrough with /dev/tpmrm0?


     Stefan