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Re: [PATCH v2 4/5] arm/mpu: Implement ioremap_attr for MPU
- To: Hari Limaye <Hari.Limaye@xxxxxxx>
- From: "Orzel, Michal" <michal.orzel@xxxxxxx>
- Date: Thu, 28 Aug 2025 11:41:47 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "Luca Fancellu" <Luca.Fancellu@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Thu, 28 Aug 2025 09:42:00 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 28/08/2025 11:37, Hari Limaye wrote:
> Hi Michal,
>
>>>
>>> + rc = mpumap_contains_region(xen_mpumap, max_mpu_regions, start, end,
>>> &idx);
>>> + if ( rc < 0 )
>>> + panic("Cannot handle overlapping MPU memory protection
>>> regions\n");
>> Why panic? This function is not used only at boot time and should propagate
>> error to the caller, it's also within a spin lock.
>
> Good point - I will update this to propagate the error in the next version of
> the series.
>
>>> + /* This API is only meant to unmap transient regions */
>>> + if ( !region_is_transient(&xen_mpumap[idx]) )
>> So is this the only purpose of the transient flag? To check that
>> unmap_mm_range
>> is used on the range that was mapped with map_mm_range? What would happen
>> without introducing this flag? You already check for the matching attributes.
>>
>> ~Michal
>>
>
> Yes this is the purpose of the transient flag - we want to ensure that a call
> to unmap_mm_range only destroys a mapping that was created by a matching call
> to map_mm_range. Due to the fact that map_mm_range may not create a mapping
> in the instance that one already exists - `/* Already mapped with same
> attributes */` - we need this check to ensure that unmap_mm_range will not
> destroy a pre-existing mapping.
Ok, understood.
~Michal
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