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Re: [PATCH v7 3/5] xen/arm64: mm: Introduce helpers to prepare/enable/disable the identity mapping
- To: Julien Grall <julien@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Michal Orzel <michal.orzel@xxxxxxx>
- Date: Mon, 17 Apr 2023 09:55:54 +0200
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- Cc: <Luca.Fancellu@xxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, "Stefano Stabellini" <sstabellini@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Mon, 17 Apr 2023 07:56:12 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16/04/2023 16:32, Julien Grall wrote:
>
>
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> In follow-up patches we will need to have part of Xen identity mapped in
> order to safely switch the TTBR.
>
> On some platform, the identity mapping may have to start at 0. If we always
> keep the identity region mapped, NULL pointer dereference would lead to
> access to valid mapping.
>
> It would be possible to relocate Xen to avoid clashing with address 0.
> However the identity mapping is only meant to be used in very limited
> places. Therefore it would be better to keep the identity region invalid
> for most of the time.
>
> Two new external helpers are introduced:
> - arch_setup_page_tables() will setup the page-tables so it is
> easy to create the mapping afterwards.
> - update_identity_mapping() will create/remove the identity mapping
>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
~Michal
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