Re: [Xen-devel] [PATCH v6 09/10] tools/arm: tee: add "tee" option for xl.cfg

[Julien Grall <julien.grall@xxxxxxx>]

On 18/06/2019 12:19, Volodymyr Babchuk wrote:
> Hi Julien,
Hi,

> Julien Grall writes:
> > > +
> > > +=item B<optee>
> > > +
> > > +Allow a guest to use OP-TEE. Note that a virtualization-aware OP-TEE
> > > +is required for this. If this option is selected, guest will be able
> > OOI, what happen if OP-TEE does not support virtualization. Will Xen
> > forbid to use it?
> Yes, Xen will get an error from OP-TEE during domain construction. This
> will lead to domain creation failure.
This is a bit odd. It means we have no way to know in advance whether OP-TEE 
will be able to create a client. In other word, when the mediator is built in 
Xen, all existing setup with OP-TEE (and no-virtualization) will fail.
My expectation is Xen should be able to know whether the mediator can be used.

> > > +to access to the real OP-TEE OS running on the host. Guest creation
> > s/real// it is redundant with the rest of the sentence. However, it
> > does not really answer to the question regarding isolation.
> Your assumption is correct - OP-TEE provides isolation on its side.
>
> > > +will fail if OP-TEE have no resources for a new guest. Number of supported
> > > +guests depends on OP-TEE configuration.
> > How about the following description (correct me if my understanding is
> > wrong):
> >
> > "Allow a guest to access the host OP-TEE OS. Xen will mediate the
> > access to OP-TEE and the resource isolation will be provided directly
> > by OP-TEE. OP-TEE itself may limit the number of guests that can
> > concurrently use it. This requires a virtualization-aware OP-TEE for
> > this to work.
> >
> > This feature is a B<technology preview>."
> That's much better than my version. Thank you.
>
> > How can a user know whether OP-TEE supports virtualization? Is it
> > configurable at build?
> Yes, there is a special configuration option CFG_VIRTUALIZATION. This is
> covered in OP-TEE documentation at [1]
>
> [1] https://optee.readthedocs.io/architecture/virtualization.html
Do we expect the link to be stable? If so, then I think a link in the 
documentation would be useful.
Cheers,

--
Julien Grall

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