Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 24 May 2021 21:21:47 +0100
From:   Will Deacon <will@kernel.org>
To:     Qais Yousef <qais.yousef@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Marc Zyngier <maz@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Quentin Perret <qperret@google.com>, Tejun Heo <tj@kernel.org>,
        Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>, kernel-team@android.com
Subject: Re: [PATCH v6 02/21] arm64: Allow mismatched 32-bit EL0 support
Message-ID: <20210524202146.GC15545@willie-the-truck>
References: <20210518094725.7701-1-will@kernel.org>
 <20210518094725.7701-3-will@kernel.org>
 <20210521152255.tosr4jwok6cjg6sf@e107158-lin.cambridge.arm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210521152255.tosr4jwok6cjg6sf@e107158-lin.cambridge.arm.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Precedence: bulk

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@kernel.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