Hi Sandeep,
Your question is very valid and we're discussing options internally.
We will come back to you with a consolidated answer shortly.
Regards, Olivier.
________________________________________ From: Sandeep Tripathy Sent: Monday, September 28, 2020 05:28 To: Soby Mathew Cc: Dan Handley; tf-a@lists.trustedfirmware.org; nd; Olivier Deprez Subject: Re: [TF-A] Query SPD/SPMD behavior with EHF
Thanks Soby and Dan for confirmation on TSPD. I can see a few more gaps in the related area.
"The EL3 interrupts (G0 interrupts) should be able to pre-empt Fast SMC i.e. any execution context for that matter ". This should apply to all SPDs including SPMD. However I learned from @Oliver that SPMD/SPMC design traps FIQs to S_EL2.
In that case a RAS interrupt can be masked by S_EL2 software (eg: Hafnium). Probably by design it will be ensured that S_EL2 will never mask the physical FIQ ?
S_EL2 FIQ handler will exit to EL3/SPMD by SMC call. And depending on the pending interrupt type either it can exit to NWd OR invoke el3 fiq vector handler synchronously ?
Are there limitations if we trap fiq to EL3 instead ?
Thanks Sandeep On Fri, Sep 18, 2020 at 6:26 PM Soby Mathew Soby.Mathew@arm.com wrote:
Hi Sandeep
Except during yielding SMC ‘disable_intr_rm_local(INTR_TYPE_NS, SECUE);’ is in effect. Intention is to avoid NS interrupt preempt secure execution (Fast SMC). But I think that will also disable G0 interrupt as both NS interrupt and G0 interrupt are on FIQ. EHF already ensures this by GIC PMR adjustment. So disabling routing model seems unnecessary in this case. This is my understanding from the code please confirm if this is correct.
The EL3 interrupts (G0 interrupts) should be able to pre-empt Fast SMC. Hence the usage of GIC PMR to mask the NS interrupts. As Dan says, the TSP_NS_INTR_ASYNC_PREEMPT predates the EHF design and it seems there is a problem as you describe.
EHF already ensures this by GIC PMR adjustment. So disabling routing model seems unnecessary in this case. This is my understanding from the code please confirm if this is correct.
You are right. Routing model manipulation is not required when EL3 interrupts are present as GIC PMR manipulation should take care of the required behaviour for yielding vs atomic SMC. You also need to ensure it works as expected when EL3 interrupts are not enabled and when EHF is disabled.
Best Regards Soby Mathew
-----Original Message----- From: TF-A tf-a-bounces@lists.trustedfirmware.org On Behalf Of Sandeep Tripathy via TF-A Sent: 17 September 2020 16:53 To: Dan Handley Dan.Handley@arm.com Cc: tf-a@lists.trustedfirmware.org Subject: Re: [TF-A] Query TSPD behavior with EHF
Hi Dan, I am not sure if this is mentioned anywhere in any documents but I think EHF handlers should be able to preempt all execution contexts at lower ELs and lower ELs should never be able to mask such interrupts. If the behavioral expectation is set the implementation can be fixed.
Thanks Sandeep
On Thu, Sep 17, 2020 at 7:57 PM Dan Handley via TF-A <tf- a@lists.trustedfirmware.org> wrote:
A correction...
-----Original Message----- From: TF-A tf-a-bounces@lists.trustedfirmware.org On Behalf Of Dan Handley via TF-A Sent: 17 September 2020 15:14
I want to handle something similar in OP-TEED along with EHF depending on
what is the expected behavior.
Hmm, I thought OP-TEED was more like the
TSP_NS_INTR_ASYNC_PREEMPT=0
case, where NS interrupts are routed to S-EL1 while processing a yielding SMC in S- EL1? Perhaps that's a better TSPD config for you to
follow?
Sorry, if EL3_EXCEPTION_HANDLING=1 then obviously NS interrupts are
routed to EL3 first, but the TSPD re-enables NS interrupts before handing over to the TSP to handle yielding calls, via a call to ehf_allow_ns_preemption.
Right, that is the case for yielding SMC handling where both NS interrupts and EL3/G0 interrupts can preempt the S_EL1/S_EL2 context. But I would expect the same routing model even for 'Fast SMC' unlike what is happening in TSPD.
Dan.
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Olivier Deprez