[PATCH 05/12] arm64: cpufeature: Detect E2H0 not being implemented

[Oliver Upton]

On Mon, Nov 13, 2023 at 05:42:37PM +0000, Marc Zyngier wrote:
> FEAT_E2H0 is a new feature that indicates whether or not HCR_EL2.E2H
> can be set to 0. Amusingly, this feature is set to 0 when implemented,
> and otherwise negative.
> 
> Add a new capability and detection infrastructure to detect the
> absence of FEAT_E2H0.
> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>

Reviewed-by: Oliver Upton <oliver.upton at linux.dev>

> ---
>  arch/arm64/kernel/cpufeature.c | 7 +++++++
>  arch/arm64/tools/cpucaps       | 1 +
>  2 files changed, 8 insertions(+)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 41db7f993eef..e0d64e8b4851 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -2787,6 +2787,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>  		.matches = has_cpuid_feature,
>  		ARM64_CPUID_FIELDS(ID_AA64MMFR2_EL1, EVT, IMP)
>  	},
> +	{
> +		.desc = "FEAT_E2H0 not implemented",
> +		.capability = ARM64_HCR_E2H_RES1,

I did read this a couple times before the neurons that interpret "0 not
implemented" and "RES1" fired together, heh.

--
Thanks,
Oliver