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RE: [PATCH v7 4/5] xen/arm64: mm: Rework switch_ttbr()
- To: Julien Grall <julien@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Henry Wang <Henry.Wang@xxxxxxx>
- Date: Mon, 17 Apr 2023 04:59:12 +0000
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- Cc: Luca Fancellu <Luca.Fancellu@xxxxxxx>, "michal.orzel@xxxxxxx" <michal.orzel@xxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Luca Fancellu <Luca.Fancellu@xxxxxxx>
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- Thread-topic: [PATCH v7 4/5] xen/arm64: mm: Rework switch_ttbr()
Hi Julien,
> -----Original Message-----
> Subject: [PATCH v7 4/5] xen/arm64: mm: Rework switch_ttbr()
>
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> At the moment, switch_ttbr() is switching the TTBR whilst the MMU is
> still on.
>
> Switching TTBR is like replacing existing mappings with new ones. So
> we need to follow the break-before-make sequence.
>
> In this case, it means the MMU needs to be switched off while the
> TTBR is updated. In order to disable the MMU, we need to first
> jump to an identity mapping.
>
> Rename switch_ttbr() to switch_ttbr_id() and create an helper on
> top to temporary map the identity mapping and call switch_ttbr()
> via the identity address.
>
> switch_ttbr_id() is now reworked to temporarily turn off the MMU
> before updating the TTBR.
>
> We also need to make sure the helper switch_ttbr() is part of the
> identity mapping. So move _end_boot past it.
>
> The arm32 code will use a different approach. So this issue is for now
> only resolved on arm64.
>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
> Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
I used the test method described in my notes from patch#2, and this
patch passed the test, so:
Tested-by: Henry Wang <Henry.Wang@xxxxxxx>
Kind regards,
Henry
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