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Date:   Fri, 4 Feb 2022 10:29:28 +0100
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Valentin Schneider <valentin.schneider@arm.com>
Cc:     linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-rt-users@vger.kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Ingo Molnar <mingo@kernel.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
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        Josh Triplett <josh@joshtriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
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        Ard Biesheuvel <ardb@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for
 migratability
Message-ID: <Yfzx+P3jUXA0Z/Y7@linutronix.de>
References: <20220127192437.1192957-1-valentin.schneider@arm.com>
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On 2022-01-27 19:24:37 [+0000], Valentin Schneider wrote:
> arch_faults_on_old_pte() relies on the calling context being
> non-preemptible. CONFIG_PREEMPT_RT turns the PTE lock into a sleepable
> spinlock, which doesn't disable preemption once acquired, triggering the
> warning in arch_faults_on_old_pte().
> 
> It does however disable migration, ensuring the task remains on the same
> CPU during the entirety of the critical section, making the read of
> cpu_has_hw_af() safe and stable.
> 
> Make arch_faults_on_old_pte() check cant_migrate() instead of preemptible().
> 
> Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> Link: https://lore.kernel.org/r/20210811201354.1976839-5-valentin.schneider@arm.com

Let me pick that up so I can drop the other two. I hope the ARM64 folks
follow my lead ;)

Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Sebastian