Re: [PATCH v5 3/5] xen/arm64: mm: Introduce helpers to prepare/enable/disable the identity mapping

[Julien Grall <julien@xxxxxxx>]

Hi Henry,

On 28/01/2023 04:54, Henry Wang wrote:
> > -----Original Message-----
> > Subject: [PATCH v5 3/5] xen/arm64: mm: Introduce helpers to
> > prepare/enable/disable the identity mapping
> >
> > 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: Henry Wang <Henry.Wang@xxxxxxx>
> With some nits below that can definitely be fixed on commit.
I need to resend a new version of this patch. So I will fix them at the 
same time and...
> Tested on FVP in Arm64 mode, so:
> Tested-by: Henry Wang <Henry.Wang@xxxxxxx>
.. didn't keep these tags.

Cheers,

--
Julien Grall