linux-kernel - Re: [PATCH v7 2/4] arm64: Add BBM Level 2 cpu feature

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Message-ID: <20250619085701.GA10805@e133081.arm.com>
Date: Thu, 19 Jun 2025 09:57:01 +0100
From: Mikołaj Lenczewski <miko.lenczewski@....com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: yang@...amperecomputing.com, catalin.marinas@....com, will@...nel.org,
	jean-philippe@...aro.org, robin.murphy@....com, joro@...tes.org,
	maz@...nel.org, oliver.upton@...ux.dev, joey.gouly@....com,
	james.morse@....com, broonie@...nel.org, ardb@...nel.org,
	baohua@...nel.org, suzuki.poulose@....com, david@...hat.com,
	jgg@...pe.ca, nicolinc@...dia.com, jsnitsel@...hat.com,
	mshavit@...gle.com, kevin.tian@...el.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev
Subject: Re: [PATCH v7 2/4] arm64: Add BBM Level 2 cpu feature

On Wed, Jun 18, 2025 at 03:07:41PM +0100, Ryan Roberts wrote:
> On 17/06/2025 10:51, Mikołaj Lenczewski wrote:
> >  #ifdef CONFIG_ARM64_PAN
> >  static void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused)
> >  {
> > @@ -2980,6 +3015,11 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
> >  		.matches = has_cpuid_feature,
> >  		ARM64_CPUID_FIELDS(ID_AA64MMFR2_EL1, EVT, IMP)
> >  	},
> > +	{
> > +		.capability = ARM64_HAS_BBML2_NOABORT,
> > +		.type = ARM64_CPUCAP_EARLY_LOCAL_CPU_FEATURE,
> > +		.matches = has_bbml2_noabort,
> 
> Is there a reason you have removed the .desc from this? Without it, the kernel
> won't print a "detected" line when it enables the feature. Previously you had:
> 
> 		.desc = "BBM Level 2 without conflict abort",
> 
> > +	},
> >  	{
> >  		.desc = "52-bit Virtual Addressing for KVM (LPA2)",
> >  		.capability = ARM64_HAS_LPA2, 
>

Damn it! I completely forgot to birng that back. Yet another remenant of
the NO_BBML2_NOABORT version we had discussed in v6, because a
description field would have been confusing due to the double negation:

https://lore.kernel.org/all/83d1f7af-3dc7-45f9-94f3-8a0917c051d2@arm.com/

Thank you very much for spotting this Ryan! Ill return the description,
and respin on Monday (unless it is possible to do this as a RESEND or
similar, but I doubt it since this is technically a functional change) :/

-- 
Kind regards,
Mikołaj Lenczewski