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

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Message-ID: <20151002074721.GA16538@pd.tnic>
Date:	Fri, 2 Oct 2015 09:47:21 +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 Fri, Oct 02, 2015 at 12:58:02AM +0000, 河合英宏 / KAWAI，HIDEHIRO wrote:
> > On Thu, Oct 01, 2015 at 10:24:19AM +0000, 河合英宏 / KAWAI，HIDEHIRO wrote:
> > > But how do we check if the starting kernel is a dump capture kernel?
> > 
> > How does that first kernel pass info to the capture kernel?
> 
> As I described in the previous mail,

I meant: "How does the first kernel pass info to the capture kernel by
*not* using the kernel command line"?

The kernel command line is not the channel to pass data to the kdump
kernel.

> Yes, your first kernel doesn't get external NMIs, but basically
> you don't have to set "noextnmi" option to the first kernel.

So it doesn't belong there as a kernel command line parameter in the
first place.

IOW, you need a different method to pass data to the second kernel. Be
it an ELF header, be it a shared page, whatever.

-- 
Regards/Gruss,
    Boris.

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