linux-kernel - Re: [V4 PATCH 4/4] x86/apic: Introduce noextnmi boot option

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Date:	Tue, 13 Oct 2015 22:22:58 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
cc:	Jonathan Corbet <corbet@....net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vivek Goyal <vgoyal@...hat.com>, linux-doc@...r.kernel.org,
	x86@...nel.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [V4 PATCH 4/4] x86/apic: Introduce noextnmi boot option

On Fri, 25 Sep 2015, Hidehiro Kawai wrote:

> This patch introduces new boot option "noextnmi" which disables
> external NMI.  This option is useful for the dump capture kernel
> so that an HA application or administrator wouldn't mistakenly
> shoot down the kernel by NMI.
> 
> Currently, only x86 supports this option.

You might add that is can be used for debugging purposes as
well. External NMIs can be their own source of trouble. :)
 
> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Jonathan Corbet <corbet@....net>
> ---
>  Documentation/kernel-parameters.txt |    4 ++++
>  arch/x86/kernel/apic/apic.c         |   17 ++++++++++++++++-
>  2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 22a4b68..8bcaccd 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2379,6 +2379,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			noexec=on: enable non-executable mappings (default)
>  			noexec=off: disable non-executable mappings
>  
> +	noextnmi	[X86]
> +			Mask external NMI.  This option is useful for a
> +			dump capture kernel to be shot down by NMI.

That should read: "...not to be shot down", right?

Other than that.

Acked-by: Thomas Gleixner <tglx@...utronix.de>
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