Re: [Xen-devel] [RFC 0/4] TEE mediator framework + OP-TEE mediator

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi,

Just answering to dom0 been 1:1 domain.

On 24/10/17 22:33, Stefano Stabellini wrote:
> On Tue, 24 Oct 2017, Volodymyr Babchuk wrote:
> > > For this series, I think we need a way to specify which domains can talk
> > > to TEE, so that we can only allow it for a specific subset of DomUs. I
> > > would probably use XSM for that.
> > I am afraid, this is not possible. As other domains aren't 1:1 mapped,
> > I need to have special translation code in mediator. Actually, I'm
> > writing it rigth now to test my changes in OP-TEE. But event this is
> > not enought for decent OP-TEE support.
> > What can be done right now: 100% Dom0-only support with vanilla
> > OP-TEE (i.e. no virtualization support in OP-TEE is needed). This is
> > even simplier task, so I can throw out some code from this patch
> > series. On other hand, in the future this will lead to sutiation when
> > two mediators for the same TEE shall be supported: one, simple, in
> > XEN, another, fully-functional in stubdom.
> I think it is fine to support OP-TEE only in Dom0 to begin with.
>
> Ideally, it would be in Dom0 for convenience and speed and the OP-TEE
> capability would be specified as an XSM label. Ideally, it would not be
> only in Dom0 because it is tied to the 1:1 map, but I understand now
> that it is a requirement. I still think that the XSM label would be good
> to have even if today it cannot be changed as only Dom0 is 1:1.
I thought a bit more about Dom0 been a 1:1 domain. It is only true for 
Device Memory and the initial RAM allocated for Dom0.
Dom0 may balloon out some pages because it has to map region belonging 
to other domain. Those regions will not be 1:1 mapped and translation 
will be needed if used.
The problem is very similar to DMA in dom0. I can't see any reason to 
not use those regions with OP-TEE. Am I wrong here?
Cheers,

--
Julien Grall

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