[PATCH v2 1/3] KVM: arm64: Make ID_AA64MMFR1_EL1.HCX writable from userspace

[Oliver Upton]

On Tue, Sep 09, 2025 at 11:44:13AM +0800, Jinqian Yang wrote:
> Allow userspace to downgrade HCX in ID_AA64MMFR1_EL1. Userspace can
> only change this value from high to low.
> 
> Signed-off-by: Jinqian Yang <yangjinqian1 at huawei.com>

I'm not sure our quality of emulation is that great in this case. We
have no way of trapping the register and it is always stateful. Better
yet, our RESx infrastructure doesn't account for the presence of
FEAT_HCX and we happily merge the contents with the host's HCRX.

We should make a reasonable attempt at upholding the architecture before
allowing userspace to de-feature FEAT_HCX.

Thanks,
Oliver