Re: [PATCH v1 1/8] docs: documentation and schema for the new TPM Proxy device
On 5/11/20 8:28 AM, Daniel P. Berrangé wrote:
On Mon, May 11, 2020 at 08:26:53AM -0300, Daniel Henrique Barboza
wrote:
>
>
> On 5/11/20 6:57 AM, Daniel P. Berrangé wrote:
>> On Mon, May 11, 2020 at 11:22:57AM +1000, David Gibson wrote:
> [...]
>>> It's a different guest side interface, the H_TPM_COMM hypercall
>>> instead of the other PAPR TPM interface. To which "why?" is a
very
>>> good question, but it's there now, so there's not much we can do
about
>>> it.
>>
>> That's ok. Even though its a different guest interface, it is still
>> conceptually a TPM device at a high level, so we should be reusing
>> the existing <tpm> device type. At most we should add a new backend
>> type
>
> I think adding a new backend type is sensible. Re-using the passthrough type
> and making the differentiation with 'model', for a device that doesn't
> operate exactly as a regular vTPM but can coexist with other vTPM devices,
> will make for a lot of IFs in the code.
Currently libvirt only allows a single <tpm>, but we can trivially
lift that restriction to allow multiple if desired too.
I don't believe it'll be necessary. Since it's only this TPM Proxy device
that
can coexist with other TPMs, my idea is to do what I did here in this series,
but instead of creating a new device type I'll re-use the existing TPM device
in a 'tpmproxy' pointer in the domain for this case.
I'll still thinking about whether a new backend type is warranted or not. For
this PPC64 case alone it'll be simpler to just add a new 'model' called
'spapr-tpm'-proxy' for the existing TPM passthrough type. Creating a new
backend type makes it easier to add other TPM Proxy devices when other archs
implement it though.
Thanks,
DHB
Regards,
Daniel