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Re: [PATCH v2 3/4] xen/arm64: allow to make aarch32 support optional
- To: Julien Grall <julien@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
- Date: Fri, 5 Sep 2025 12:34:25 +0300
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Fri, 05 Sep 2025 09:34:57 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Hi Julien,
On 05.09.25 10:04, Julien Grall wrote:
Hi Grygorii,
On 06/08/2025 10:49, Grygorii Strashko wrote:
From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
Now Arm64 AArch32 guest support is always enabled and built-in while not
all Arm64 platforms supports AArch32 (for exmaple on Armv9A) or this
typo s/exmaple/example/
ok
support might not be needed (Arm64 AArch32 is used quite rarely in embedded
systems).
More over, when focusing on safety certification, AArch32 related
code in Xen leaves a gap in terms of coverage that cannot really be
justified in words. This leaves two options: either support it (lots of
additional testing, requirements and documents would be needed) or compile
it out.
To clarify my understanding, what you are removing is support for 32-bit EL1.
But 32-bit EL0 will still be supported. Is that correct?
Yes. The 32-bit EL0 is still supported
(and was tested by creating domain with AArch64 kernel and AArch32 EL0 rootfs).
I will update Kconfig description.
[...]
- do not expose EL1 AArch32 support to guest in ID_AA64PFR0_EL1 reg if
AArch32 is disabled.
A guest is not allowed to switch bitness. So I am not sure why we need to hide
EL1.
I can drop code chunk which changes ID_AA64PFR0_EL1. Right?
Depending on the answer above, you might need to hide EL0 and have more code
(TBC) to prevent 32-bit EL0 running.
EL0 is supported.
Thank you for you comments.
--
Best regards,
-grygorii
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