Re: [PATCH v6 2/9] arm64: report address tag when FEAT_MTE_TAGGED_FAR is supported

[Yeo Reum Yun]

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@xxxxxxxxxx; will@xxxxxxxxxx; Anshuman Khandual; Joey Gouly; Yury Khrustalev; maz@xxxxxxxxxx; oliver.upton@xxxxxxxxx; frederic@xxxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; surenb@xxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx
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.