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Date: Fri, 18 May 2012 08:46:01 +0200
From: Ingo Molnar <mingo@kernel.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Tony Luck <tony.luck@intel.com>, Thomas Gleixner <tglx@linutronix.de>,
        Fenghua Yu <fenghua.yu@intel.com>, Ingo Molnar <mingo@elte.hu>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Asit K Mallick <asit.k.mallick@intel.com>,
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        linux-pm <linux-pm@vger.kernel.org>, x86 <x86@kernel.org>,
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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()
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* H. Peter Anvin <hpa@zytor.com> wrote:

> On 05/14/2012 05:17 AM, Ingo Molnar wrote:
> > 
> > * Tony Luck <tony.luck@intel.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