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Re: [PATCH v3 1/7] arm/mpu: Introduce MPU memory region map structure
- To: "Orzel, Michal" <Michal.Orzel@xxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Mon, 14 Apr 2025 15:21:00 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Penny Zheng <Penny.Zheng@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>
- Delivery-date: Mon, 14 Apr 2025 15:21:48 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH v3 1/7] arm/mpu: Introduce MPU memory region map structure
Hi Michal,
> On 14 Apr 2025, at 16:01, Orzel, Michal <Michal.Orzel@xxxxxxx> wrote:
>
>
>
> On 14/04/2025 16:50, Luca Fancellu wrote:
>> Hi Michal,
>>
>>> On 14 Apr 2025, at 11:17, Orzel, Michal <michal.orzel@xxxxxxx> wrote:
>>>
>>>
>>>
>>> On 11/04/2025 16:56, Luca Fancellu wrote:
>>>> From: Penny Zheng <Penny.Zheng@xxxxxxx>
>>>>
>>>> Introduce pr_t typedef which is a structure having the prbar
>>>> and prlar members, each being structured as the registers of
>>>> the aarch64 armv8-r architecture.
>>>>
>>>> Introduce the array 'xen_mpumap' that will store a view of
>>>> the content of the MPU regions.
>>>>
>>>> Introduce MAX_MPU_REGIONS macro that uses the value of
>>>> NUM_MPU_REGIONS_MASK just for clarity, because using the
>>>> latter as number of elements of the xen_mpumap array might
>>>> be misleading.
>>> What should be the size of this array? I thought NUM_MPU_REGIONS indicates
>>> how
>>> many regions there can be (i.e. 256) and this should be the size. Yet you
>>> use
>>> MASK for size which is odd.
>>
>> So the maximum number of regions for aarch64 armv8-r are 255,
>> MPUIR_EL2.REGION is an
>> 8 bit field advertising the number of region supported.
> So there can be max 255 regions. Ok.
>
>>
>> Is it better if I use just the below?
>>
>> #define MAX_MPU_REGIONS 255
> If there are 255 regions, what NUM_MPU_REGIONS macro is for which stores 256?
> These two macros confuse me. Or is it that by your macro you want to denote
> the
> max region number? In that case, the macro should be named MAX_MPU_REGION_NR
> or
> alike.
I know, NUM_MPU_REGIONS should have a different name as it’s a bit misleading,
ok
I’ll name the macro I use here as MAX_MPU_REGION_NR.
Cheers,
Luca
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