Hello, Tomi again,

We have 2 Nordic platforms and suppose nRF5340 is one of them (need double check) so we shall be able to build and run it.

Unfortunately, I cannot promise to jump into the problem immediately but want to prepare when time permits.

 

Regards,

Anton

 

From: Fontanilles, Tomi <tomi.fontanilles@nordicsemi.no>
Sent: Tuesday, October 22, 2024 12:31 PM
To: tf-m@lists.trustedfirmware.org; Anton Komlev <Anton.Komlev@arm.com>
Subject: Re: [TF-M] Re: increased interrupt latency when calling the PSA PS API

 

Hi Anton,

Thanks for your answer.

 

I could provide you with the test application, but it requires you to have the nRF Connect SDK set up to be able to build and run it.

Also, running it requires either an nRF5340 or an nRF54L15. It's likely possible to reproduce the issue on at least other Nordic devices that support TF-M (e.g. nRF91).

Are you able to run it somehow? Or do you just want to be able to build it?

 

On Tue, 2024-10-22 at 11:22 +0000, Anton Komlev wrote:

Hello Tomi,

 

Thank you for reporting this issue. Let’s look into it together.

Could you please share the details of your test environment : the build command(s) and the test application (if possible)?

 

Best regards,

Anton

 

From: Fontanilles, Tomi via TF-M <tf-m@lists.trustedfirmware.org>
Sent: Tuesday, October 22, 2024 9:30 AM
To: tf-m@lists.trustedfirmware.org
Subject: [TF-M] Re: increased interrupt latency when calling the PSA PS API

 

A small update on the increase numbers. As said latency increase varies, but I do sometimes observe an even bigger increase.

The base maximum interrupt latency observed is 9μs (under normal conditions, when not calling the PSA PS API), and it sometimes jumps as high as 400μs (when calling it). So that's an almost 50-fold increase.

So there can apparently be quite a bit of fluctuation in the maximum latency increase. Basically between ~90μs (10-fold increase) up to ~400μs (50-fold increase).

 

Also, as additional information, there is nothing going on in parallel (in the application). This is all happening in a simple application made for reproducing the issue.

 

 

On Tue, 2024-10-22 at 07:37 +0000, Fontanilles, Tomi via TF-M wrote:

Hi all,

 

I'm currently looking into an issue reported internally where the maximum latency for a zero-latency, priority 0 interrupt dramatically increases during a call to the PSA Protected Storage (PS) API.

The maximum interrupt latency goes up ~10-fold, or even some more at times (it varies), and this is not acceptable to code running on the NS side for normal operation.

 

It's as simple as calling psa_ps_set(1, 4, buf, PSA_STORAGE_FLAG_NONE) once.

During that call (which I am told was also seen to be unreasonably long: 600ms for 4 bytes, 1s for 1000 bytes), the maximum interrupt latency goes up.

It (the maximum) seems to not vary too much even if increasing the size of stored assets (tested up to 4000 bytes), though it can get up to 20 times higher than the normal interrupt latency.

 

Also, other functions were tested (psa_generate_random(),psa_hash_compute()).

Those don't provoke an increased interrupt latency. Maybe it's only about the PS, or maybe some other calls can provoke that as well.

 

Does someone have an explanation for that?

And even more importantly, can that interrupt latency be reduced, ideally down to normal levels?

 

Thanks in advance.

Tomi