linux-kernel - Re: [PATCH v5 1/5] arm64: Add framework to turn IPI as NMI

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Date:   Mon, 19 Oct 2020 12:56:25 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, tglx@...utronix.de,
        jason@...edaemon.net, mark.rutland@....com,
        julien.thierry.kdev@...il.com, dianders@...omium.org,
        daniel.thompson@...aro.org, jason.wessel@...driver.com,
        msys.mizuma@...il.com, ito-yuichi@...itsu.com,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/5] arm64: Add framework to turn IPI as NMI

On 2020-10-14 12:12, Sumit Garg wrote:
> Introduce framework to turn an IPI as NMI using pseudo NMIs. In case a
> particular platform doesn't support pseudo NMIs, then request IPI as a
> regular IRQ.
> 
> The main motivation for this feature is to have an IPI that can be
> leveraged to invoke NMI functions on other CPUs. And current 
> prospective
> users are NMI backtrace and KGDB CPUs round-up whose support is added
> via future patches.
> 
> Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
> ---
>  arch/arm64/include/asm/nmi.h | 16 +++++++++
>  arch/arm64/kernel/Makefile   |  2 +-
>  arch/arm64/kernel/ipi_nmi.c  | 77 
> ++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 94 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/nmi.h
>  create mode 100644 arch/arm64/kernel/ipi_nmi.c

[...]

> +	irq_set_status_flags(ipi, IRQ_HIDDEN);

Another thing is this. Why are you hiding this from /proc/interrupts?
The only reason the other IPIs are hidden is that displaying them as
"normal" interrupts would be a change in userspace ABI.

In your case, this is something new that can perfectly appear as
a standard interrupt (and I don't see how you'd display the
statistics otherwise).

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