Re: [PATCH] firmware: arm_sdei: pass sdei_api_event_register right parameters

[James Morse]

Hello!

(sorry for the delayed response)

On 10/09/2021 05:01, Liguang Zhang wrote:
> Function _local_event_enable is used for private sdei event
> registeration called by sdei_event_register. We should pass

(registration)

> sdei_api_event_register right flag and mpidr parameters, otherwise atf
> may trigger assert errors.

> diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
> index a7e762c352f9..0736752dadde 100644
> --- a/drivers/firmware/arm_sdei.c
> +++ b/drivers/firmware/arm_sdei.c
> @@ -558,14 +558,16 @@ static int sdei_api_event_register(u32 event_num, unsigned long entry_point,
>  static void _local_event_register(void *data)
>  {
>  	int err;
> +	u64 mpidr;
>  	struct sdei_registered_event *reg;
>  	struct sdei_crosscall_args *arg = data;
>  
>  	WARN_ON(preemptible());
>  
> +	mpidr = read_cpuid_mpidr();
>  	reg = per_cpu_ptr(arg->event->private_registered, smp_processor_id());
>  	err = sdei_api_event_register(arg->event->event_num, sdei_entry_point,
> -				      reg, 0, 0);
> +				      reg, SDEI_EVENT_REGISTER_RM_PE, mpidr);

Hmmm, this looks like a bug in TFA.

5.1.2.2 "Parameters" of DEN 0054B has:
| Routing mode is valid only for a shared event. For a private event, the routing mode is
| ignored.

Worse, the mpidr field has:
| Currently the format is defined only when the selected routing mode is RM_PE.


Over in trusted firmware land:

https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/tree/services/std_svc/sdei/sdei_main.c?h=v2.5#n361

| static int64_t sdei_event_register(int ev_num,
| 				uint64_t ep,
| 				uint64_t arg,
| 				uint64_t flags,
|				uint64_t mpidr)
| {

|	/* Private events always target the PE */
|	if (is_event_private(map))
|		flags = SDEI_REGF_RM_PE;

It looks like this re-uses the 'caller specified the routing' code, but didn't update the
mpidr.


You mention TFA takes an assert failure, I assume that brings the machine down.
(Presumably you don't have a CPU with an affinity of zero.)

Does this mean no-one relies on this, and we can fix the firmware?
(I'll go report this to the relevant folk)


Thanks!

James


>  
>  	sdei_cross_call_return(arg, err);
>  }
>