Re: [PATCH v12 5/7] arm64: smp: IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI

From: Mark Rutland <mark.rutland@arm.com>
To: Douglas Anderson <dianders@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Sumit Garg <sumit.garg@linaro.org>,
	Daniel Thompson <daniel.thompson@linaro.org>,
	Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	Masayoshi Mizuma <msys.mizuma@gmail.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Chen-Yu Tsai <wens@csie.org>,
	Lecopzer Chen <lecopzer.chen@mediatek.com>,
	Tomohiro Misono <misono.tomohiro@fujitsu.com>,
	Stephane Eranian <eranian@google.com>,
	kgdb-bugreport@lists.sourceforge.net,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Stephen Boyd <swboyd@chromium.org>,
	ito-yuichi@fujitsu.com, linux-perf-users@vger.kernel.org,
	Ard Biesheuvel <ardb@kernel.org>,
	D Scott Phillips <scott@os.amperecomputing.com>,
	Josh Poimboeuf <jpoimboe@kernel.org>,
	Valentin Schneider <vschneid@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v12 5/7] arm64: smp: IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI
Date: Thu, 31 Aug 2023 11:12:34 +0100	[thread overview]
Message-ID: <ZPBnkkDc9GSxrjmC@FVFF77S0Q05N> (raw)
In-Reply-To: <20230830121115.v12.5.Ifadbfd45b22c52edcb499034dd4783d096343260@changeid>

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@arm.com>
> Reviewed-by: Stephen Boyd <swboyd@chromium.org>
> Reviewed-by: Misono Tomohiro <misono.tomohiro@fujitsu.com>
> Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
> Signed-off-by: Douglas Anderson <dianders@chromium.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@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.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
> 