Re: [PATCH v6 04/12] x86/smpboot.c: Don't offline CPU0 if any irqcan not be migrated out of it and remove CPU0 check in smp_callin()

[H. Peter Anvin]

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

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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