Re: [Xen-devel] [PATCH v2 04/13] optee: add OP-TEE mediator skeleton

[Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>]

Hi Julien,

On 04.09.18 22:48, Julien Grall wrote:
> On 09/03/2018 06:55 PM, Volodymyr Babchuk wrote:
> > Hi Julien,
> Hi Volodymyr,
>
> > On 03.09.18 20:38, Julien Grall wrote:
> > > Hi Volodymyr,
> > >
> > > On 03/09/18 17:54, Volodymyr Babchuk wrote:
> > > > Add very basic OP-TEE mediator. It can probe for OP-TEE presence,
> > > > tell it about domain creation/destuction and forward all known
> > > s/destuction/destruction/
> > >
> > > > calls.
> > > >
> > > > This is all what is needed for Dom0 to work with OP-TEE as long
> > > > as Dom0 shares 1:1 mapped pages with OP-TEE. Any attempt to call
> > > > OP-TEE from DomU will fail and can lead to spectacular results.
> > > Shall we expect fireworks? :).
> > I tried couple of time, but with no success :)
> >
> > > Anyway, I think this is a call for forbidding DomU access until it is 
> > > supported. This also has the benefits to allow merging Dom0 support 
> > > for OP-TEE without the rest.
> > Some time ago you said that I can't be sure that Dom0 is 1:1 mapped, 
> > because of grant refs. So, actually, any access should be forbidden. I 
> > can omit
> Oh right. I that case, make it clear in the commit message because there 
> are nothing in Dom0 preventing to share page that are not direct mapped.
> This will make easier for the commiter (either Stefano or I) to know 
> this can't go without the rest of the series.
Ah, sure. Had to indicate this explicitly. Will do this in the next 
version of the series.
[...]
> > > > +                  &resp);
> > > > +
> > > > +    set_user_reg(regs, 0, resp.a0);
> > > > +    set_user_reg(regs, 1, resp.a1);
> > > > +    set_user_reg(regs, 2, resp.a2);
> > > > +    set_user_reg(regs, 3, resp.a3);
> > > > +    set_user_reg(regs, 4, 0);
> > > > +    set_user_reg(regs, 5, 0);
> > > > +    set_user_reg(regs, 6, 0);
> > > > +    set_user_reg(regs, 7, 0);
> > > > +}
> > > > +
> > > > +static void optee_domain_destroy(struct domain *d)
> > > > +{
> > > > +    struct arm_smccc_res resp;
> > > > +
> > > > +    /* At this time all domain VCPUs should be stopped */
> > > > +
> > > > +    /* Inform OP-TEE that domain is shutting down */
> > > > +    arm_smccc_smc(OPTEE_SMC_VM_DESTROYED, d->domain_id + 1, 0, 0, 
> > > > 0, 0, 0, 0,
> > > > +                  &resp);
> > > So this SMC should never fail or even get preempted? I was kind of 
> > > expecting that it may time some time to destroy a domain.
> > It is the fast SMCCC call, so it can't be preempted. And it is really 
> > fast, at lest in OP-TEE case.
> Without number, I can't really know what fast means here. Do you have a 
> rough idea?
"Fast" used there in a sense, defined in SMCCC:

"
Fast Calls execute atomic operations.

The call appears to be atomic from the perspective of the calling PE, 
and returns when the requested
operation has completed."

And "Standard Call" (will be introduced in the series) is the "Yielding 
Call". Probably I should use term from SMCCC, but for some reason I 
stick to term used it OP-TEE.
I can do some measurements on how "fast" this particular call is. But 
problem is that it is really atomic from OP-TEE perspective.

--
Volodymyr Babchuk

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