linux-kernel - Re: [PATCH v22 2/5] arm64: el2_setup.h: Make __init_el2

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Message-ID: <aDiBuC2JjAUNDq29@e133380.arm.com>
Date: Thu, 29 May 2025 17:25:13 +0100
From: Dave Martin <Dave.Martin@....com>
To: Rob Herring <robh@...nel.org>
Cc: Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	James Clark <james.clark@...aro.org>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Leo Yan <leo.yan@....com>, linux-arm-kernel@...ts.infradead.org,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, kvmarm@...ts.linux.dev
Subject: Re: [PATCH v22 2/5] arm64: el2_setup.h: Make __init_el2_fgt labels
 consistent, again

Hi,

On Thu, May 22, 2025 at 12:20:35PM -0500, Rob Herring wrote:
> On Thu, May 22, 2025 at 11:15 AM Dave Martin <Dave.Martin@....com> wrote:
> >
> > On Tue, May 20, 2025 at 05:27:37PM -0500, Rob Herring (Arm) wrote:
> > > From: Anshuman Khandual <anshuman.khandual@....com>
> > >
> > > Commit 5b39db6037e7 ("arm64: el2_setup.h: Rename some labels to be more
> > > diff-friendly") reworked the labels in __init_el2_fgt to say what's
> > > skipped rather than what the target location is. The exception was
> > > "set_fgt_" which is where registers are written. In reviewing the BRBE
> > > additions, Will suggested "set_debug_fgt_" where HDFGxTR_EL2 are
> > > written. Doing that would partially revert commit 5b39db6037e7 undoing
> > > the goal of minimizing additions here, but it would follow the
> > > convention for labels where registers are written.
> > >
> > > So let's do both. Branches that skip something go to a "skip" label and
> > > places that set registers have a "set" label. This results in some
> > > double labels, but it makes things entirely consistent.
> > >
> > > While we're here, the SME skip label was incorrectly named, so fix it.
> > >
> > > Reported-by: Will Deacon <will@...nel.org>
> > > Cc: Dave Martin <Dave.Martin@....com>
> > > Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> > > ---
> > > This one can be applied even if the rest of the series is not.
> > >
> > > v22:
> > >  - New patch
> > > ---
> > >  arch/arm64/include/asm/el2_setup.h | 10 +++++++---
> > >  1 file changed, 7 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h
> > > index ebceaae3c749..30f57b0334a3 100644
> > > --- a/arch/arm64/include/asm/el2_setup.h
> > > +++ b/arch/arm64/include/asm/el2_setup.h
> > > @@ -204,19 +204,21 @@
> > >       orr     x0, x0, #(1 << 62)
> > >
> > >  .Lskip_spe_fgt_\@:
> > > +
> > > +.Lset_debug_fgt_\@:
> >
> > Dangling label?  There doesn't seem to be any branch to it in this
> > series, unless I've missed something.
> 
> I tried to explain that in the commit message. To have both what you
> wanted and what Will suggested, you end up with 2 labels in between
> the last skip and setting registers.

Hmm, I wasn't trying to advocate for adding dead labels in anticipation
of their use, just to avoid labels whose names conflict with an
anticipated future use.

I guess this is harmless, but I may look at this again as and when...

Cheers
---Dave