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Re: [PATCH v4 3/6] xen/arm: mpu: Define Xen start address for MPU systems
- To: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Mon, 28 Oct 2024 14:53:28 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Jiamei Xie <Jiamei.Xie@xxxxxxx>
- Delivery-date: Mon, 28 Oct 2024 14:53:58 +0000
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- Thread-topic: [PATCH v4 3/6] xen/arm: mpu: Define Xen start address for MPU systems
Hi Ayan,
> On 28 Oct 2024, at 12:45, Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx> wrote:
>
> From: Wei Chen <wei.chen@xxxxxxx>
>
> On Armv8-A, Xen has a fixed virtual start address (link address too) for all
> Armv8-A platforms. In an MMU based system, Xen can map its loaded address to
> this virtual start address. So, on Armv8-A platforms, the Xen start address
> does
> not need to be configurable. But on Armv8-R platforms, there is no MMU to map
> loaded address to a fixed virtual address and different platforms will have
> very
> different address space layout. So Xen cannot use a fixed physical address on
> MPU based system and need to have it configurable.
>
> So, we introduce a Kconfig option for users to set the start address. The
> start
> address needs to be aligned to 4KB. We have a check for this alignment.
>
> MPU allows us to define regions which are 64 bits aligned. This restriction
> comes from the bitfields of PRBAR, PRLAR (the lower 6 bits are 0 extended to
> provide the base and limit address of a region). This means that the start
> address of Xen needs to be at least 64 bits aligned (as it will correspond to
> the start address of memory protection region).
>
> As for now Xen on MPU tries to use the same memory alignment restrictions as
> it
> has been for MMU. We have added a build assertion to ensure that the page size
> is 4KB. Unlike MMU where the starting virtual address is 2MB, Xen on MPU needs
> the start address to be 4KB (ie page size) aligned.
>
> In case if the user forgets to set the start address, then 0xffffffff is used
> as default. This is to trigger the error (on alignment check) and thereby
> prompt
> user to set the start address.
>
> Also updated config.h so that it includes mpu/layout.h when CONFIG_MPU is
> defined.
>
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> Signed-off-by: Jiamei.Xie <jiamei.xie@xxxxxxx>
> Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
> —
Looks good to me
Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
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