Re: [PATCH v2 3/4] xen/arm64: allow to make aarch32 support optional

[Julien Grall <julien@xxxxxxx>]

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/

> 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?
[...]

> - 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. Depending on the answer above, you might need to hide EL0 
and have more code (TBC) to prevent 32-bit EL0 running.
Cheers,

--
Julien Grall