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Re: [PATCH v2 4/6] arm/mpu: Introduce modify_after_init_mappings
- To: Harry Ramsey <harry.ramsey@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: "Orzel, Michal" <michal.orzel@xxxxxxx>
- Date: Tue, 13 Jan 2026 11:37:17 +0100
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- Cc: <Luca.Fancellu@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Hari Limaye <hari.limaye@xxxxxxx>
- Delivery-date: Tue, 13 Jan 2026 10:37:56 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 05/01/2026 12:35, Harry Ramsey wrote:
> From: Luca Fancellu <luca.fancellu@xxxxxxx>
>
> During `init_done`, Xen sets the permissions of all symbols marked with
> __ro_after_init to be read-only. This does not work on MPU systems at
> present because part-region modification is not supported.
>
> Therefore introduce the function `modify_after_init_mappings` for MMU
> and MPU, to handle the divergent approaches to setting permissions of
> __ro_after_init symbols.
>
> For MPU systems `modify_xen_mappings` will shrink the RW mapping on one
> side and extend the RO mapping on the other. This approach prevents
> wasting an additional region between RW and RO mappings.
>
> As the new function is marked with __init, it needs to be called before
> `free_init_memory`.
>
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> Signed-off-by: Hari Limaye <hari.limaye@xxxxxxx>
> Signed-off-by: Harry Ramsey <harry.ramsey@xxxxxxx>
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
~Michal
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