Re: [PATCH v5 1/2] arm64: Add feature detection for fine grained traps

From: Zenghui Yu <zenghui.yu@linux.dev>
To: Mark Brown <broonie@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>
Cc: Joey Gouly <joey.gouly@arm.com>,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev
Subject: Re: [PATCH v5 1/2] arm64: Add feature detection for fine grained traps
Date: Sun, 16 Jul 2023 22:44:01 +0800	[thread overview]
Message-ID: <d5d26d8e-e1ba-b6a2-0643-f3a6c2c667d4@linux.dev> (raw)
In-Reply-To: <20230712-kvm-arm64-fgt-v5-1-dae3ec236288@kernel.org>

On 2023/7/12 20:50, Mark Brown wrote:
> In order to allow us to have shared code for managing fine grained traps
> for KVM guests add it as a detected feature rather than relying on it
> being a dependency of other features.
> 
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
>  arch/arm64/kernel/cpufeature.c | 11 +++++++++++
>  arch/arm64/tools/cpucaps       |  1 +
>  2 files changed, 12 insertions(+)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index f9d456fe132d..0768f98c49cc 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -2627,6 +2627,17 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>  		.matches = has_cpuid_feature,
>  		ARM64_CPUID_FIELDS(ID_AA64ISAR1_EL1, LRCPC, IMP)
>  	},
> +	{
> +		.desc = "Fine Grained Traps",
> +		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
> +		.capability = ARM64_HAS_FGT,
> +		.sys_reg = SYS_ID_AA64MMFR0_EL1,
> +		.sign = FTR_UNSIGNED,
> +		.field_pos = ID_AA64MMFR0_EL1_FGT_SHIFT,
> +		.field_width = 4,
> +		.min_field_value = 1,
> +		.matches = has_cpuid_feature,
> +	},

Any reason not to use the ARM64_CPUID_FIELDS() helper?

Zenghui