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

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Message-ID: <20151005082704.GA23259@nazgul.tnic>
Date:	Mon, 5 Oct 2015 10:27:04 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	河合英宏 / KAWAI，HIDEHIRO 
	<hidehiro.kawai.ez@...achi.com>
Cc:	'Peter Zijlstra' <peterz@...radead.org>,
	Jonathan Corbet <corbet@....net>,
	Ingo Molnar <mingo@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vivek Goyal <vgoyal@...hat.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>
Subject: Re: [V4 PATCH 4/4] x86/apic: Introduce noextnmi boot option

On Mon, Oct 05, 2015 at 02:03:58AM +0000, 河合英宏 / KAWAI，HIDEHIRO wrote:
> That's different from my point of view.  I'm not going to pass
> some data from the first kernel to the second kernel. I'm just going to
> provide a configurable option for the second kernel to users.

Dude, WTF?! You're adding a kernel command line which is supposed to
be used *only* by the kdump kernel. But nooo, it is there in the open
and visible to people. And anyone can type it in during boot. AND THAT
SHOULDN'T BE POSSIBLE IN THE FIRST PLACE!

This information is strictly for the kdump kernel - it shouldn't be a
generic command line option. How hard it is to understand that simple
fact?!

<snip obvious use case>

> I think we should use the ELF header only if the passed information
> is saved to a crash dump.

So what?! ELF header will contain the additional bit of information that
the second kernel wasn't reacting to NMIs. But that's fine, that *is*
the desired behavior anyway.

All I'm saying is, this is a strict kdump kernel "command", so to speak,
and it doesn't belong with the generic kernel command line parameters.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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