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Date:   Mon, 24 May 2021 13:09:59 +0100
From:   Will Deacon <will@kernel.org>
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Qais Yousef <qais.yousef@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: <20210524120959.GB14913@willie-the-truck>
References: <20210518094725.7701-1-will@kernel.org>
 <20210518094725.7701-3-will@kernel.org>
 <20210521104155.GC6675@arm.com>
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On Fri, May 21, 2021 at 11:41:56AM +0100, Catalin Marinas wrote:
> On Tue, May 18, 2021 at 10:47:06AM +0100, Will Deacon wrote:
> > +static int enable_mismatched_32bit_el0(unsigned int cpu)
> > +{
> > +	struct cpuinfo_arm64 *info = &per_cpu(cpu_data, cpu);
> > +	bool cpu_32bit = id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0);
> > +
> > +	if (cpu_32bit) {
> > +		cpumask_set_cpu(cpu, cpu_32bit_el0_mask);
> > +		static_branch_enable_cpuslocked(&arm64_mismatched_32bit_el0);
> 
> It may be worth only calling static_branch_enable_cpuslocked() if not
> already set, in case you try this on a system with lots of CPUs.

static_key_enable_cpuslocked() already checks this early on, so I don't
think we need another check here (note that we're not calling stop_machine()
here _anyway_; the '_cpuslocked' suffix just says that we're already holding
cpu_hotplug_lock via the notifier).

Will