linux-kernel - Re: [PATCH v4] arm64: mm: Make arch_faults_on_old

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Date:   Fri, 4 Feb 2022 10:29:28 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rt-users@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Steven Price <steven.price@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Mike Galbraith <efault@....de>
Subject: Re: [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for
 migratability

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@...utronix.de>
> Signed-off-by: Valentin Schneider <valentin.schneider@....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@...utronix.de>

Sebastian