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

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Message-ID: <20210524202146.GC15545@willie-the-truck>
Date:   Mon, 24 May 2021 21:21:47 +0100
From:   Will Deacon <will@...nel.org>
To:     Qais Yousef <qais.yousef@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Morten Rasmussen <morten.rasmussen@....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 Fri, May 21, 2021 at 04:22:55PM +0100, Qais Yousef wrote:
> On 05/18/21 10:47, Will Deacon wrote:
> > When confronted with a mixture of CPUs, some of which support 32-bit
> > applications and others which don't, we quite sensibly treat the system
> > as 64-bit only for userspace and prevent execve() of 32-bit binaries.
> > 
> > Unfortunately, some crazy folks have decided to build systems like this
> > with the intention of running 32-bit applications, so relax our
> > sanitisation logic to continue to advertise 32-bit support to userspace
> > on these systems and track the real 32-bit capable cores in a cpumask
> > instead. For now, the default behaviour remains but will be tied to
> > a command-line option in a later patch.
> > 
> > Signed-off-by: Will Deacon <will@...nel.org>
> > ---
> >  arch/arm64/include/asm/cpucaps.h    |   3 +-
> 
> Heads up. I just tried to apply this on 5.13-rc2 and it failed because cpucaps.
> was removed; it's autogenerated now.
> 
> See commit 0c6c2d3615ef: ()"arm64: Generate cpucaps.h")

Yup, cheers. I'll sort that out once we're at the stage where we're merging
patches.

Will