Re: [Xen-devel] [PATCH v4 09/10] tools/arm: tee: add "tee" option for xl.cfg

[Julien Grall <julien.grall@xxxxxxx>]

Hi Achin,

On 18/03/2019 21:04, Achin Gupta wrote:
> On Mon, Mar 18, 2019 at 03:49:12PM +0000, Julien Grall wrote:
> > (+ Achin)
> >
> > On 07/03/2019 21:04, Volodymyr Babchuk wrote:
> > > From: Volodymyr Babchuk <vlad.babchuk@xxxxxxxxx>
> > >
> > > This enumeration controls TEE type for a domain. Currently there is
> > > two possible options: either 'none' or 'native'.
> > >
> > > 'none' is the default value and it basically disables TEE support at
> > > all.
> > >
> > > 'native' enables access to a "real" TEE installed on a platform.
> > I am aware I made that suggestion. But I think the naming is not ideal
> > between the user and the toolstack. The question is how this is going to fit
> > with the S-EL2 feature where multiple TEE can run together?
> >
> > I have CCed Achin to see he has any vision how this could be interfaced.
> Thanks.
>
> Multiple TEEs (or rather Trusted OSs) can coexist on Armv8.3 and earlier. They
> will not be isolated but play along nicely.
That's interesting. So, in the current case (i.e without SPCI), how do you 
communicate with a specific Trusted OS?
> The intent is that prior to S-EL2 and multiple TOSs, each TOS will migrate to
> using the SPCI spec. At this stage, there should be no need for a TOS specific
> mediator in the Hypervisor. IOW, there should be a "generic" SPCI
> mediator. Maybe, we can add a TEE type 'generic' later to enable access to any
> TEE through this generic interface?
Yes, that's probably a good option to add later. So maybe renaming 'native' to 
'optee'(or 'op-tee') would be more suitable here. This avoid the ambiguity of 
'native'.
> Support for multiple TOSs has raised other questions that we are trying to
> address e.g. dependencies between them or on guests in Nwd, impact on scheduling
> decisions made by Nwd etc. Support for OP-TEE in this patch stack does not need
> to answer these just yet it seems. It is more likely that we will have to tackle
> support for multiple TEEs afresh rather than treating it as an extension of
> support for a specific TOS.
I totally agree. SPCI is a separate topic, although I wanted to get a more 
suitable name for the config so we can avoid introduce a new option later on.
> Happy to discuss further and I hope this helps in some way.
Thank you for the feedback!

Cheers,

--
Julien Grall

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