I reported the same problem earlier and was told that this was by design.

Earlier thread:
https://lists.trustedfirmware.org/archives/list/tf-m@lists.trustedfirmware.org/thread/CEHFBMY6AG67GAVZJ2LY4OUHNBEDAMII/#CEHFBMY6AG67GAVZJ2LY4OUHNBEDAMII

-Joakim

From: Bohdan.Hunko--- via TF-M <tf-m@lists.trustedfirmware.org>
Sent: mandag 13. mars 2023 15:17
To: tf-m@lists.trustedfirmware.org
Cc: Roman.Mazurak@infineon.com
Subject: [TF-M] Scheduler problem

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Hi everyone,

Why investigation some interrupts related stuff I have noticed a problem/bug in the scheduler.

PendSV_Handler has following code:

" movs r0, #"M2S(EXC_RETURN_SECURE_STACK)" \n"

" mov r1, lr \n"

" tst r0, r1 \n" /* NS interrupted */

" beq v8b_pendsv_exit \n" /* No schedule */

Which means that if NSPE was interrupted then no scheduling will be done. This created a problem in following scenario:

NSPE is executing
Secure interrupts arrives.
NSPE is interrupted, secure interrupt is handled.
Secure interrupts triggers scheduling of some partition.
Secure interrupt returns
Scheduling is triggered
PendSV returns (because /* NS interrupted */ /* No schedule */ ) and does not perform scheduling even thought pending partition is present. This means that pending partition will only be scheduled when next PSA call will be done be NSPE. Even if there would be subsequent Secure interrupts that preempt NSPE, partition will not be scheduled because PendSV will always return without scheduling because NSPE was interrupted.

I was not able to find any information about this in TFM docs so I assume this is a bug.

Please let me know if I am wrong. And if this is real problem then is there a plan to fix this?

Regards,

Bohdan Hunko

Cypress Semiconductor Ukraine

Engineer

CSUKR CSS ICW SW FW

Mobile: +38099 50 19 714
Bohdan.Hunko@infineon.com