Re: [PATCH v3 1/6] arm/mpu: Find MPU region by range

[Hari Limaye <Hari.Limaye@xxxxxxx>]

Hi Michal,

> On 15 Jul 2025, at 09:45, Orzel, Michal <michal.orzel@xxxxxxx> wrote:
> 
> 
> 
> On 15/07/2025 10:36, Hari Limaye wrote:
>> Hi Michal,
>> 
>>>> +int mpumap_contains_region(pr_t *table, uint8_t nr_regions, paddr_t base,
>>>> +                           paddr_t limit, uint8_t *index)
>>>> +{
>>>> +    ASSERT(index);
>>>> +    *index = INVALID_REGION_IDX;
>>>> +
>>>> +    /*
>>>> +     * The caller supplies a half-open interval [base, limit), i.e. limit 
>>>> is the
>>>> +     * first byte *after* the region. Require limit strictly greater than 
>>>> base,
>>>> +     * which is necessarily a non-empty region.
>>>> +     */
>>>> +    ASSERT(base < limit);
>>> Well, that does not guarantee a non-empty region.
>>> Consider passing [x, x+1). The assert will pass, even though the region is 
>>> empty.
>>> 
>>> ~Michal
>>> 
>> 
>> Apologies, I may well be missing something here! Please could you suggest a 
>> code snippet to understand your expectation here / what you would prefer the 
>> assert to be?
>> 
>> As I understand it, with a half-open interval [base, limit) as is passed to 
>> this function, the size is  `limit - base` and so the region [x, x+1) will 
>> have size 1. The empty region starting at the same address would be [x, x). 
>> But perhaps I am making the off-by-one error here.
> Hmm, I think I made a mistake here. Region of size 1B would have base == limit
> in registers. All good then.
> 
> ~Michal
> 

Thanks for double checking. I notice you did not add your tag here, I wanted to 
check if you think this patch is reviewed from your perspective?

Many thanks,
Hari