Re: [PATCH 3/3] firmware/shim: UNSUPPORTED=n

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.05.2021 16:39, Roger Pau Monné wrote:
> On Fri, Apr 30, 2021 at 04:45:03PM +0200, Jan Beulich wrote:
>> We shouldn't default to include any unsupported code in the shim. Mark
>> the setting as off, replacing the ARGO specification. This points out
>> anomalies with the scheduler configuration: Unsupported schedulers
>> better don't default to Y in release builds (like is already the case
>> for ARINC653). Without these adjustments, the shim would suddenly build
>> with RTDS as its default scheduler.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks.

>> ----
>> I'm certainly open to consider alterations on the sched/Kconfig
>> adjustments, but _something_ needs to be done there. In particular I'm
>> puzzled to find the NULL scheduler marked unsupported. Clearly with
>> the shim defaulting to it, it must be supported at least there.
> 
> Indeed, I think we should mark NULL as supported for the shim usage
> (which is very specific anyway, because it manages a single domain).

George, Dario, what is your position towards null's support status?

>> --- a/xen/common/sched/Kconfig
>> +++ b/xen/common/sched/Kconfig
>> @@ -16,7 +16,7 @@ config SCHED_CREDIT2
>>  
>>  config SCHED_RTDS
>>      bool "RTDS scheduler support (UNSUPPORTED)" if UNSUPPORTED
>> -    default y
>> +    default DEBUG
> 
> I would also be fine with leaving the default as 'n' for unsupported
> features.

So would I be; I merely didn't want to make too big of step by
going straight from y to n. George, Dario - you're the maintainers
of this code (and I'd need your ack anyway), do you have any
preference?

>> @@ -31,7 +31,7 @@ config SCHED_ARINC653
>>  
>>  config SCHED_NULL
>>      bool "Null scheduler support (UNSUPPORTED)" if UNSUPPORTED
>> -    default y
>> +    default PV_SHIM || DEBUG
> 
> Do we need the pvshim_defconfig to set CONFIG_SCHED_NULL=y after this?

I don't think so, the default will be y for it. Explicit settings
are needed only when we want a non-default value.

Jan