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Re: [PATCH v4 13/14] xen/arm64: mm: Rework switch_ttbr()
- To: Julien Grall <julien@xxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Fri, 13 Jan 2023 16:50:38 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Fri, 13 Jan 2023 16:51:13 +0000
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- Thread-topic: [PATCH v4 13/14] xen/arm64: mm: Rework switch_ttbr()
> On 13 Jan 2023, at 10:11, Julien Grall <julien@xxxxxxx> wrote:
>
> 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>
The sequence looks ok to me, also the reasoning about barriers and
register dependencies discussed in the previous version.
Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
I’ve also built for arm32/64 and test this patch on fvp, booting Dom0
and creating/running/destroying some guests
Tested-by: Luca Fancellu <luca.fancellu@xxxxxxx>
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