linux-kernel - Re: [PATCH v6 04/12] x86/smpboot.c: Don't offline CPU0 if any irq can not be migrated out of it and remove CPU0 check in smp

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Message-ID: <20120518064601.GC429@gmail.com>
Date:	Fri, 18 May 2012 08:46:01 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Tony Luck <tony.luck@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Fenghua Yu <fenghua.yu@...el.com>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Asit K Mallick <asit.k.mallick@...el.com>,
	Arjan Dan De Ven <arjan@...ux.intel.com>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Len Brown <len.brown@...el.com>,
	"Srivatssa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Chen Gong <gong.chen@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...r.kernel.org>, x86 <x86@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v6 04/12] x86/smpboot.c: Don't offline CPU0 if any irq
 can not be migrated out of it and remove CPU0 check in smp_callin()


* H. Peter Anvin <hpa@...or.com> wrote:

> On 05/14/2012 05:17 AM, Ingo Molnar wrote:
> > 
> > * Tony Luck <tony.luck@...el.com> wrote:
> > 
> >> Biggest code impact of that is the extra code to bring cpu0 
> >> back online using NMI instead of INIT. We can't use INIT 
> >> because if cpu0 gets one, it just resets the whole machine :-( 
> >> But obviously we'd like to avoid special cases where there is 
> >> a sane way to do so.
> > 
> > Could we just standardize on NMI bringup during regular bootup?
> > 
> 
> The first instance has to be SIPI because you can't give the 
> CPU an NMI without the IDT being setup.  We *could* assume 
> that the processor is parked in real mode with the valid 
> real-mode IDT set up (in which case the vector at physical 
> address 8 applies) but that seems to assume a lot from the 
> BIOS for little gain.  In particular I suspect that UEFI-based 
> BIOSes may very well park the CPU in protected or long mode.

Ok, fair enough.

Thanks,

	Ingo
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