Subject: Re: [PATCH 0/3] KVM: arm64: FEAT_{S1POE,ATS1A} support fixes

From: Joey Gouly <[email-masked]>
Date: Wed, 3 Jun 2026 11:41:42 +0100

On Tue, Jun 02, 2026 at 04:54:26PM +0100, Marc Zyngier wrote:
> Whilst working on a slightly unrelated feature (FEAT_NV3), I found out
> that an L2 guest wouldn't boot if the host was exposed to FEAT_S1POE.
> 
> Upon investigation (and hours wasted in a SW model), it became
> apparent that while the AT S1E1A code was ready for action, it had
> never been fully plugged in (blame the usual suspect...).
> 
> This resulted in an extremely odd failure mode, with an L2 being
> unable to make forward progress, but KVM at L1 not taking the hint
> that something was really wrong. Additionally, an embarrassing typo
> was spotted in the CPTR_EL2 handling.
> 
> With this in, FEAT_S1POE no longer breaks our NV guests.
> 
> Marc Zyngier (3):
>   KVM: arm64: Key CPTR_EL2.E0POE propagation on FEAT_S1POE
>   KVM: arm64: Wire AT S1E1A in the system instruction handling table
>   arm64: cpufeature: Expose ID_AA64ISAR2_EL1.ATS1A to KVM
> 
>  arch/arm64/kernel/cpufeature.c          | 1 +
>  arch/arm64/kvm/hyp/include/hyp/switch.h | 2 +-
>  arch/arm64/kvm/sys_regs.c               | 1 +
>  3 files changed, 3 insertions(+), 1 deletion(-)

Reviewed-by: Joey Gouly <[email-masked]>

Thanks,
Joey