Re: [PATCH v5 2/3] arm/mpu: Introduce `v8r_el1_msa` device tree property for domains

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 11-May-26 13:07, Luca Fancellu wrote:
> Hi Michal,
> 
>>>
>>>>>>> +
>>>>>>> +static inline bool v8r_el1_msa_domain_sanitise_config(
>>>>>>> +    const struct xen_domctl_createdomain *config)
>>>>>> Why can't this function be common? I can see 3 definitions (Arm64 MPU, 
>>>>>> Arm32
>>>>>> MPU, MMU) but they do not have anything that would prevent from 
>>>>>> generalizing
>>>>>> them in a single function.
>>>>>
>>>>> I can do a common one I think, just to be aligned, should the common one 
>>>>> behaves as the current implementation?
>>>>>
>>>>> Arm64/32 MMU: Only v8r_el1_msa == XEN_DOMCTL_CONFIG_ARM_V8R_EL1_MSA_NONE 
>>>>> allowed
>>>>> Arm64: Only v8r_el1_msa == 
>>>>> XEN_DOMCTL_CONFIG_ARM_V8R_EL1_MSA_{NONE,PMSA,VMSA}  allowed
>>>>> Arm32: Only v8r_el1_msa == XEN_DOMCTL_CONFIG_ARM_V8R_EL1_MSA_{NONE,PMSA}  
>>>>> allowed
>>>> What's the reason for allowing NONE for MPU here? None denotes property not
>>>> specified but at this point it should be set to a default.
>>>
>>> We treat NONE as PMSA on Armv8-R, so either NONE and PMSA are valid and 
>>> lead to PMSA at EL1
>> NONE denotes property not set i.e. set a default. IMO at the place where we 
>> set
>> a default, NONE should be switched to PMSA. This is a cleaner solution than
>> giving two options the same meaning. Sanitization could then verify that 
>> indeed
>> the default setting took place.
> 
> Ok so this is a bit different from how all other *_NONE are handled currently 
> (TEE and SCI).
> 
> So on MPU Arm32/64 now we will stop the domain creation if NONE is passed, is 
> that the behaviour
> you are expecting for DOMCTL v8r_el1_msa? (Ideally we should not get this 
> because we will switch
> during DT parse)
I think the confusion is that you are mixing the meaning of none (i.e. I don't
want it) with not set. In case of TEE and SCI, none means you I don't want TEE
or SCI, please disable them. Now, how would this look like for MPU. I don't want
PMSA or VMSA? This does not make any sense because it's something impossible.

~Michal