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

On 5/12/20 1:44 PM, Daniel P. Berrangé wrote: > On Tue, May 12, 2020 at 01:21:40PM -0300, Daniel Henrique Barboza wrote: > > > > > > On 5/12/20 12:53 PM, Daniel P. Berrangé wrote: > > > On Tue, May 12, 2020 at 11:21:52AM -0400, Stefan Berger wrote: > > > > On 5/11/20 7:28 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. > > > > > > > > > > > > QEMU won't accept multiple TIS or CRB devices, though. > > > > > > The commit message says you can do 2 at a time: > > > > > > "Although redundant, there is currently no technical > > > limitation for a guest to assign both a vTPM and a TPM Proxy at the > > > same time." > > > > > > is that text not accurate ? > > > > > > It is. A TPM Proxy is not considered a TIS or CRB, so it's ok to mix it up > > with another TPM device. The allowed combinations are: > > > > - single vTPM device > > - single TPM Proxy device > > - a single vTPM + single TPM Proxy devices > > So we do need multiple <tpm> support in the XML for this last case > then. Indeed we do. Working on it ATM. The plan is for this kind of XML format to be valid: <tpm model='tpm-tis'> <backend type='passthrough'> <device path='/dev/tpm0'/> </backend> </tpm> <tpm model='spapr-tpm-proxy'> <backend type='passthrough'> <device path='/dev/tpmrm0'/> </backend> </tpm>