linux-kernel - Re: [PATCH v12 5/7] arm64: smp: IPI_CPU_STOP and IPI_CPU_CRASH

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Date:   Thu, 31 Aug 2023 11:12:34 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Masayoshi Mizuma <msys.mizuma@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        Tomohiro Misono <misono.tomohiro@...itsu.com>,
        Stephane Eranian <eranian@...gle.com>,
        kgdb-bugreport@...ts.sourceforge.net,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <swboyd@...omium.org>, ito-yuichi@...itsu.com,
        linux-perf-users@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        D Scott Phillips <scott@...amperecomputing.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 5/7] arm64: smp: IPI_CPU_STOP and IPI_CPU_CRASH_STOP
 should try for NMI

On Wed, Aug 30, 2023 at 12:11:26PM -0700, Douglas Anderson wrote:
> There's no reason why IPI_CPU_STOP and IPI_CPU_CRASH_STOP can't be
> handled as NMI. They are very simple and everything in them is
> NMI-safe. Mark them as things to use NMI for if NMI is available.
> 
> Suggested-by: Mark Rutland <mark.rutland@....com>
> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> Reviewed-by: Misono Tomohiro <misono.tomohiro@...itsu.com>
> Reviewed-by: Sumit Garg <sumit.garg@...aro.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> I don't actually have any good way to test/validate this patch. It's
> added to the series at Mark's request.

I've just sent out an LKDTM test that can be used to test this:

  http://lore.kernel.org/lkml/20230831101026.3122590-1-mark.rutland@arm.com

So FWIW:

Acked-by: Mark Rutland <mark.rutland@....com>
Tested-by: Mark Rutland <mark.rutland@....com>

Mark.

> 
> (no changes since v10)
> 
> Changes in v10:
> - ("IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI") new for v10.
> 
>  arch/arm64/kernel/smp.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 28c904ca499a..800c59cf9b64 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -946,6 +946,8 @@ static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
>  		return false;
>  
>  	switch (ipi) {
> +	case IPI_CPU_STOP:
> +	case IPI_CPU_CRASH_STOP:
>  	case IPI_CPU_BACKTRACE:
>  		return true;
>  	default:
> -- 
> 2.42.0.283.g2d96d420d3-goog
>