linux-kernel - Re: [PATCH v6 02/21] arm64: Allow mismatched 32-bit EL0 support

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Date:   Mon, 24 May 2021 14:49:21 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Will Deacon <will@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Qais Yousef <qais.yousef@....com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Quentin Perret <qperret@...gle.com>, Tejun Heo <tj@...nel.org>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, kernel-team@...roid.com
Subject: Re: [PATCH v6 02/21] arm64: Allow mismatched 32-bit EL0 support

On Mon, May 24, 2021 at 01:05:50PM +0100, Will Deacon wrote:
> On Fri, May 21, 2021 at 11:25:23AM +0100, Catalin Marinas wrote:
> > On Tue, May 18, 2021 at 10:47:06AM +0100, Will Deacon wrote:
> > > +static bool has_32bit_el0(const struct arm64_cpu_capabilities *entry, int scope)
> > > +{
> > > +	if (!has_cpuid_feature(entry, scope))
> > > +		return allow_mismatched_32bit_el0;
> > > +
> > > +	if (scope == SCOPE_SYSTEM)
> > > +		pr_info("detected: 32-bit EL0 Support\n");
> > > +
> > > +	return true;
> > > +}
> > 
> > We may have discussed this before: AFAICT this will print 32-bit EL0
> > detected even if there's no 32-bit EL0 on any CPU. Should we instead
> > print 32-bit EL0 detected on CPU X when allow_mismatched_32bit_el0 is
> > passed? It would also give us an indication of the system configuration
> > when people start reporting bugs.
> 
> The function above only runs if we've detected 32-bit support via
> aa64pfr0_el1, so I think we're ok. We also have a print when we detect the
> mismatch (see enable_mismatched_32bit_el0()).

It makes sense, you removed the .desc from the arm64_features entry as
well.

Reviewed-by: Catalin Marinas <catalin.marinas@....com>