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Re: [PATCH v2 4/6] arm/mpu: Destroy an existing entry in Xen MPU memory mapping table
- To: Hari Limaye <Hari.Limaye@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: "Orzel, Michal" <michal.orzel@xxxxxxx>
- Date: Mon, 14 Jul 2025 09:25:24 +0200
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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: Mon, 14 Jul 2025 07:25:44 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 11/07/2025 08:04, Hari Limaye wrote:
> 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.
I don't have a strong preference here. I think we can keep your current
solution.
~Michal
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