linux-kernel - Re: [PATCH v6 1/5] arm64: cpufeature: add FEAT

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Message-ID: <aJ9vW8SgklYByjpB@arm.com>
Date: Fri, 15 Aug 2025 18:33:15 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: will@...nel.org, broonie@...nel.org, maz@...nel.org,
	oliver.upton@...ux.dev, shameerali.kolothum.thodi@...wei.com,
	joey.gouly@....com, james.morse@....com, ardb@...nel.org,
	scott@...amperecomputing.com, suzuki.poulose@....com,
	yuzenghui@...wei.com, mark.rutland@....com,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/5] arm64: cpufeature: add FEAT_LSUI

On Mon, Aug 11, 2025 at 05:36:31PM +0100, Yeoreum Yun wrote:
> @@ -3131,6 +3132,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>  		.matches = has_cpuid_feature,
>  		ARM64_CPUID_FIELDS(ID_AA64PFR2_EL1, GCIE, IMP)
>  	},
> +	{
> +		.desc = "Unprivileged Load Store Instructions (LSUI)",
> +		.capability = ARM64_HAS_LSUI,
> +		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
> +		.matches = has_cpuid_feature,
> +		ARM64_CPUID_FIELDS(ID_AA64ISAR3_EL1, LSUI, IMP)
> +	},
>  	{},
>  };

Since this is only used in the kernel, I wonder whether we should hide
it behind #ifdef CONFIG_AS_HAS_LSUI. Otherwise we report it as present
and one may infer that the kernel is going to use it. Not a strong view
and I don't think we have a precedent for this.

-- 
Catalin