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Re: [PATCH v7 2/5] xen/arm64: Rework the memory layout
- To: Julien Grall <julien@xxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Mon, 17 Apr 2023 07:21:27 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "michal.orzel@xxxxxxx" <michal.orzel@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 07:22:30 +0000
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- Thread-topic: [PATCH v7 2/5] xen/arm64: Rework the memory layout
> On 16 Apr 2023, at 15:32, Julien Grall <julien@xxxxxxx> wrote:
>
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> Xen is currently not fully compliant with the Arm Arm because it will
> switch the TTBR with the MMU on.
>
> In order to be compliant, we need to disable the MMU before
> switching the TTBR. The implication is the page-tables should
> contain an identity mapping of the code switching the TTBR.
>
> In most of the case we expect Xen to be loaded in low memory. I am aware
> of one platform (i.e AMD Seattle) where the memory start above 512GB.
> To give us some slack, consider that Xen may be loaded in the first 2TB
> of the physical address space.
>
> The memory layout is reshuffled to keep the first four slots of the zeroeth
> level free. All the regions currently in L0 slot 0 will not be part of
> slot 4 (2TB). This requires a slight tweak of the boot code because
> XEN_VIRT_START (2TB + 2MB) cannot be used as an immediate.
>
> This reshuffle will make trivial to create a 1:1 mapping when Xen is
> loaded below 2TB.
>
> Lastly, take the opportunity to check a compile time if any of the
> regions may overlap with the reserved area for identity mapping.
>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
>
Hi Julien,
It looks fine to me.
Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
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