linux-kernel - Re: [PATCH v4 1/5] arm64: Add framework to turn IPI as NMI

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Date:   Sat, 10 Oct 2020 10:34:04 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Masayoshi Mizuma <msys.mizuma@...il.com>
Cc:     Sumit Garg <sumit.garg@...aro.org>, catalin.marinas@....com,
        will@...nel.org, mark.rutland@....com, daniel.thompson@...aro.org,
        jason@...edaemon.net, kgdb-bugreport@...ts.sourceforge.net,
        dianders@...omium.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, jason.wessel@...driver.com,
        tglx@...utronix.de, julien.thierry.kdev@...il.com
Subject: Re: [PATCH v4 1/5] arm64: Add framework to turn IPI as NMI

On Sat, 10 Oct 2020 02:58:55 +0100,
Masayoshi Mizuma <msys.mizuma@...il.com> wrote:

[...]

> > +void ipi_nmi_setup(int cpu)
> > +{
> > +	if (!ipi_desc)
> > +		return;
> 
> ipi_nmi_setup() may be called twice for CPU0:
> 
>   set_smp_ipi_range => set_smp_ipi_nmi => ipi_nmi_setup
>                     => ipi_setup => ipi_nmi_setup
> 
> Actually, I got the following error message via the second ipi_nmi_setup():
> 
>   GICv3: Pseudo-NMIs enabled using relaxed ICC_PMR_EL1 synchronisation
>   GICv3: Cannot set NMI property of enabled IRQ 8
>   genirq: Failed to setup NMI delivery: irq 8
> 
> Why don't we have a check to prevent that? Like as:
> 
>        if (cpumask_test_cpu(cpu, ipi_desc->percpu_enabled))
>                return;

That's definitely the wrong thing to do. prepare_nmi_setup() shouldn't
be called twice, and papering over it isn't acceptable.

	M.

-- 
Without deviation from the norm, progress is not possible.