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Re: [PATCH v3 3/7] arm/mpu: Introduce utility functions for the pr_t type
- To: "Orzel, Michal" <Michal.Orzel@xxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Wed, 16 Apr 2025 12:31:22 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Wed, 16 Apr 2025 12:32:07 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-index: AQHbqvIP34UccZOkWUuu+Y+Ap2U3MrOmJOcAgAAb/QA=
- Thread-topic: [PATCH v3 3/7] arm/mpu: Introduce utility functions for the pr_t type
Hi Michal,
> On 16 Apr 2025, at 11:50, Orzel, Michal <Michal.Orzel@xxxxxxx> wrote:
>
>
>
> On 11/04/2025 16:56, Luca Fancellu wrote:
>> Introduce few utility function to manipulate and handle the
>> pr_t type.
>>
>> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
>> ---
>> xen/arch/arm/include/asm/mpu.h | 40 ++++++++++++++++++++++++++++++++++
>> 1 file changed, 40 insertions(+)
>>
>> diff --git a/xen/arch/arm/include/asm/mpu.h b/xen/arch/arm/include/asm/mpu.h
>> index 59ff22c804c1..6971507457fb 100644
>> --- a/xen/arch/arm/include/asm/mpu.h
>> +++ b/xen/arch/arm/include/asm/mpu.h
>> @@ -20,6 +20,46 @@
>> #define NUM_MPU_REGIONS_MASK (NUM_MPU_REGIONS - 1)
>> #define MAX_MPU_REGIONS NUM_MPU_REGIONS_MASK
>>
>> +#ifndef __ASSEMBLY__
>> +
>> +/* Set base address of MPU protection region(pr_t). */
> What's the use of (pr_t) in this comment? pr_t is a data type. If at all, it
> would want to be ...region @pr but I think you can skip it.
ok
>
>> +static inline void pr_set_base(pr_t *pr, paddr_t base)
>> +{
>> + pr->prbar.reg.base = (base >> MPU_REGION_SHIFT);
> Looking at pr_t definition, base/limit is 46 bits wide. However the spec says
> that last 4bits are reserved (i.e. you should not write to them) unless
> FEAT_LPA
> is implemented. What's our plan here?
So we’re currently supporting max 1TB, so probably this one needs to be on the
case when FEAT_LPA is considered not implemented, so I’ll change and if we will
later support more than 42 bit we could do something?
>
>> +}
>> +
>> +/* Set limit address of MPU protection region(pr_t). */
>> +static inline void pr_set_limit(pr_t *pr, paddr_t limit)
>> +{
>> + pr->prlar.reg.limit = ((limit - 1) >> MPU_REGION_SHIFT);
> Why -1? AFAIR these registers take inclusive addresses, so is it because you
> want caller to pass limit as exclusive and you convert it to inclusive? I
> think
> it's quite error prone.
Yes it’s meant to be used with exclusive range, shall we document it or use
Inclusive range instead?
Cheers,
Luca
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