linux-kernel - Re: [PATCH v3 1/3] arm64: add FEAT_MTE_TAGGED

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Message-ID: <aBqhOCwK6zQmNd87@e129823.arm.com>
Date: Wed, 7 May 2025 00:54:32 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: will@...nel.org, broonie@...nel.org, anshuman.khandual@....com,
	joey.gouly@....com, yury.khrustalev@....com, maz@...nel.org,
	oliver.upton@...ux.dev, frederic@...nel.org,
	shmeerali.kolothum.thodi@...wei.com, james.morse@....com,
	mark.rutland@....com, huangxiaojia2@...wei.com,
	akpm@...ux-foundation.org, surenb@...gle.com, robin.murphy@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, nd@....com,
	Peter Collingbourne <pcc@...gle.com>
Subject: Re: [PATCH v3 1/3] arm64: add FEAT_MTE_TAGGED_FAR feature

Hi Catalin,

> On Thu, Apr 10, 2025 at 08:47:19AM +0100, Yeoreum Yun wrote:
> > Add FEAT_MTE_TAGGED_FAR cpucap which makes FAR_ELx report
> > all non-address bits on a synchronous MTE tag check fault since Armv8.9
> >
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> > Acked-by: Yury Khrustalev <yury.khrustalev@....com>
> [...]
> > @@ -3191,6 +3199,7 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
> >  #ifdef CONFIG_ARM64_MTE
> >  	HWCAP_CAP(ID_AA64PFR1_EL1, MTE, MTE2, CAP_HWCAP, KERNEL_HWCAP_MTE),
> >  	HWCAP_CAP(ID_AA64PFR1_EL1, MTE, MTE3, CAP_HWCAP, KERNEL_HWCAP_MTE3),
> > +	HWCAP_CAP(ID_AA64PFR2_EL1, MTEFAR, IMP, CAP_HWCAP, KERNEL_HWCAP_MTE_FAR),
>
> Nitpick: from a theoretical bisectability perspective, I'd move the
> hwcap exposing to the following patch. The rest, feature detection etc
> can stay in this file. Otherwise, one can apply this patch, see the
> hwcap but not get the actual behaviour.

Thanks. I'll squash realted HWCAP to followin patch.

> >  #endif /* CONFIG_ARM64_MTE */
> >  	HWCAP_CAP(ID_AA64MMFR0_EL1, ECV, IMP, CAP_HWCAP, KERNEL_HWCAP_ECV),
> >  	HWCAP_CAP(ID_AA64MMFR1_EL1, AFP, IMP, CAP_HWCAP, KERNEL_HWCAP_AFP),
> > diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
> > index 285d7d538342..e2b13454e38a 100644
> > --- a/arch/arm64/kernel/cpuinfo.c
> > +++ b/arch/arm64/kernel/cpuinfo.c
> > @@ -160,6 +160,7 @@ static const char *const hwcap_str[] = {
> >  	[KERNEL_HWCAP_SME_SFEXPA]	= "smesfexpa",
> >  	[KERNEL_HWCAP_SME_STMOP]	= "smestmop",
> >  	[KERNEL_HWCAP_SME_SMOP4]	= "smesmop4",
> > +	[KERNEL_HWCAP_MTE_FAR]		= "mte_far",
>
> Personal preference: "mtefar" (no underscore), mostly because there's no
> other underscore in the hwcap strings yet ;).

Thanks. I'll change it!

--
Sincerely,
Yeoreum Yun