linux-kernel - Re: [PATCH v6 2/9] arm64: report address tag when FEAT_MTE_TAGGED

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Message-ID: <c0b4dc8a-b37c-4e8e-be2e-bc8906615702@sirena.org.uk>
Date: Wed, 11 Jun 2025 12:43:18 +0100
From: Mark Brown <broonie@...nel.org>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: catalin.marinas@....com, pcc@...gle.com, will@...nel.org,
	anshuman.khandual@....com, joey.gouly@....com,
	yury.khrustalev@....com, maz@...nel.org, oliver.upton@...ux.dev,
	frederic@...nel.org, akpm@...ux-foundation.org, surenb@...gle.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 2/9] arm64: report address tag when
 FEAT_MTE_TAGGED_FAR is supported

On Wed, Jun 11, 2025 at 10:41:00AM +0100, Yeoreum Yun wrote:

> +HWCAP3_MTE_FAR
> +    Functionality implied by ID_AA64PFR2_EL1.MTEFAR == 0b0001.

> +Applications should interpret the values of these bits based on
> +the support for the 'mte_far' hwcap. If the support is not present,
> +the values of these bits should be considered as undefined otherwise valid.

The constant is HWCAP3_MTE_FAR and the cpuinfo is mtefar:

> +	[KERNEL_HWCAP_MTE_FAR]		= "mtefar",

The reference to the hwcap should probably be one of these, I'd go for
HWCAP3_MTE_FAR since it says hwcap.

>  	/*
>  	 * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN
>  	 * for tag check faults. Set them to corresponding bits in the untagged
> -	 * address.
> +	 * address if ARM64_MTE_FAR isn't supported.
> +	 * Otherwise, bits 63:60 of FAR_EL1 are KNOWN.

Should this say UNKNOWN?

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