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Date:   Tue, 20 Oct 2020 13:32:03 +0100
From:   Marc Zyngier <maz@kernel.org>
To:     Daniel Thompson <daniel.thompson@linaro.org>
Cc:     Sumit Garg <sumit.garg@linaro.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        Mark Rutland <mark.rutland@arm.com>,
        julien.thierry.kdev@gmail.com,
        Douglas Anderson <dianders@chromium.org>,
        Jason Wessel <jason.wessel@windriver.com>,
        Masayoshi Mizuma <msys.mizuma@gmail.com>,
        ito-yuichi@fujitsu.com, kgdb-bugreport@lists.sourceforge.net,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 1/5] arm64: Add framework to turn IPI as NMI
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On 2020-10-20 13:25, Daniel Thompson wrote:
> On Tue, Oct 20, 2020 at 04:52:43PM +0530, Sumit Garg wrote:

[...]

>> So in general, IPI as a normal IRQ is still useful for debugging but
>> it can't debug a core which is stuck in deadlock with interrupts
>> disabled.
>> 
>> And since we choose override default implementations for pseudo NMI
>> support, we need to be backwards compatible for platforms which don't
>> possess pseudo NMI support.
> 
> Do the fallback implementations require a new IPI? The fallbacks
> could rely on existing mechanisms such as the smp_call_function
> family.

Indeed. I'd be worried of using that mechanism for NMIs, but normal
IPIs should stick to the normal cross-call stuff.

The jury is still out on why this is a good idea, given that it
doesn't work in the only interesting case (deadlocked CPUs).

          M.
-- 
Jazz is not dead. It just smells funny...