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Re: [PATCH v2 4/6] arm/mpu: Destroy an existing entry in Xen MPU memory mapping table


  • To: "Orzel, Michal" <michal.orzel@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Hari Limaye <Hari.Limaye@xxxxxxx>
  • Date: Fri, 11 Jul 2025 06:04:25 +0000
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  • Cc: Luca Fancellu <Luca.Fancellu@xxxxxxx>, 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: Fri, 11 Jul 2025 06:05:11 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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  • Thread-topic: [PATCH v2 4/6] arm/mpu: Destroy an existing entry in Xen MPU memory mapping table

Hi Michal,

Thank you for reviewing the patch.

 

> > +    /* Zeroing the region will also zero the region enable */

> > +    memset(&xen_mpumap[index], 0, sizeof(pr_t));

> Is it ok that for a fast case (i.e. 0-31) our representation of prbar/prlar will

> be different from the HW i.e. xen_mpumap[index] is 0 vs only .en bit of prlar

> being 0 in HW?

 

I think this should not matter - there is nothing reading registers directly and

all the decisions are taken looking into xen_mpumap.

 

However, if you would prefer, we could alter the logic here to only clear the .en

bit in xen_mpumap[index] in the fast case, so that things remain consistent? Alternatively we could always directly zero the entirety of the registers, but then we would remove the use of the fast case entirely.

 

Many thanks,

Hari


 


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