Re: [Xen-devel] [RFC] WIP: optee: add OP-TEE mediator

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Stuart,

On 12/05/2017 03:36 PM, Stuart Yoder wrote:
> > > There are limit on pCPUs, though. But this is not a problem, because
> > > XEN scheduler will decide which guest will access OP-TEE right now.
> > > OP-TEE don't have own scheduler at all, by the way. It is scheduled
> > > by normal world.
> > Do you mind to give a bit more explanation here? Do you plan to add 
> > knowledge of OP-TEE in the scheduler?
> Regarding scheduling-- OP-TEE runs with interrupts enabled (generally).  
> So when an SMC
> is in process in OP-TEE and the normal OS or hypervisor timer tick 
> fires, OP-TEE halts
> the current the in-progress thread, saves states, and returns to the 
> normal world to
> let the normal world timer interrupt handler and scheduler do its normal 
> thing.  Eventually
> when the normal world thread is re-scheduled and the in-progress thread 
> restarts the
> SMC.  That process continues until the SMC is completely done. So the 
> OS/VMM scheduler
> needs no awareness of OP-TEE since OP-TEE is cooperating with the normal 
> world.
Thank you for the explanation. I see you specifically mention the 
hypervisor timer tick. How about the other interrupts? Will OP-TEE halts 
the current in-progress thread and then return to Xen/OS?
Cheers,

--
Julien Grall

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