Hi Caleb,

The quick answer to your query is to mask the NS interrupts in BL31 (option a), You should not remove the callback to OPTEE as it may need to do its own state maintained before system RESET.

There are other scenarios in PSCI (e.g. CPU power down) path which need to consider disabling NS interrupts before invoking Secure world hooks, will provide further analysis on those later.

Thanks
Manish Pandey

From: Caleb Ethridge via TF-A <tf-a@lists.trustedfirmware.org>
Sent: 10 November 2023 15:12
To: tf-a@lists.trustedfirmware.org <tf-a@lists.trustedfirmware.org>
Subject: [TF-A] Handling of normal world interrupts with BL31 PSCI handler
 
Hello,

If normal world interrupts are received while invoking TF-A's PSCI reset handler, we have observed that the reset can be aborted.
 
In TF-A's PSCI reset handler, a call out to OP-TEE is made before performing the platform-specific reset:
https://github.com/ARM-software/arm-trusted-firmware/blob/master/lib/psci/psci_system_off.c#L44
https://github.com/ARM-software/arm-trusted-firmware/blob/master/services/spd/opteed/opteed_pm.c#L233
 
When OP-TEE is entered, it is possible to receive foreign (normal world) interrupts, which invokes the procedure described here: https://optee.readthedocs.io/en/3.16.0/architecture/core.html#deliver-non-secure-interrupts-to-normal-world
When the SMC call is aborted as described above, this results in the reboot failing. Linux does not retry the PSCI reset (https://github.com/torvalds/linux/blob/master/drivers/firmware/psci/psci.c#L308). This makes sense because it is not expecting the SMC call to fail (it expected to make an uninterruptable SMC call into the secure monitor, not a call into OP-TEE).
 
If OP-TEE itself is setup to handle PSCI reset calls, it also handles them in (uninterruptable) SMC context:
https://github.com/OP-TEE/optee_os/blob/master/core/arch/arm/sm/psci.c#L140
https://github.com/OP-TEE/optee_os/blob/master/core/arch/arm/sm/sm_a32.S#L96
 
Based on this, we see two possible solutions:
a) Masking the non-secure interrupts in BL31 while we are doing a reset
b) Removing the call to OPTEE in the reset handler so that we never leave the SMC context
 
Which option do you suggest? Or are we missing an important detail here?

Thanks,

Caleb
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