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

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Message-ID:
 <GV1PR08MB105213A44E40741700202F7CFFB75A@GV1PR08MB10521.eurprd08.prod.outlook.com>
Date: Wed, 11 Jun 2025 12:19:57 +0000
From: Yeo Reum Yun <YeoReum.Yun@....com>
To: Mark Brown <broonie@...nel.org>
CC: Catalin Marinas <Catalin.Marinas@....com>, "pcc@...gle.com"
	<pcc@...gle.com>, "will@...nel.org" <will@...nel.org>, Anshuman Khandual
	<Anshuman.Khandual@....com>, Joey Gouly <Joey.Gouly@....com>, Yury Khrustalev
	<Yury.Khrustalev@....com>, "maz@...nel.org" <maz@...nel.org>,
	"oliver.upton@...ux.dev" <oliver.upton@...ux.dev>, "frederic@...nel.org"
	<frederic@...nel.org>, "akpm@...ux-foundation.org"
	<akpm@...ux-foundation.org>, "surenb@...gle.com" <surenb@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-doc@...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

Hi Mark,

> > +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.

Just for confirmation. so change to "mtefar" -> "mte_far"
Am I missing?


--  
Sincerely,
Yeoreum Yun




________________________________________
From: Mark Brown
Sent: Wednesday, June 11, 2025 12:43
To: Yeo Reum Yun
Cc: Catalin Marinas; pcc@...gle.com; will@...nel.org; Anshuman Khandual; Joey Gouly; Yury Khrustalev; 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?

I think KNOWN is corret since this is Otherwise case (when MET_FAR is supported).

Thanks.