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

[Luca Fancellu <Luca.Fancellu@xxxxxxx>]

>> 
>>>> 
>>>>>>>> +
>>>>>>>> +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.

ok makes sense, I will then:

Arm 64/32 MMU: allow only XEN_DOMCTL_CONFIG_ARM_V8R_EL1_MSA_NONE
Arm 64 MPU: allow XEN_DOMCTL_CONFIG_ARM_V8R_EL1_MSA_{PMSA,VMSA}
Arm 32 MPU: allow XEN_DOMCTL_CONFIG_ARM_V8R_EL1_MSA_PMSA

Cheers,
Luca