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()

[Ingo Molnar]

* H. Peter Anvin <hpa@xxxxxxxxx> wrote:

> 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.

Ok, fair enough.

Thanks,

	Ingo
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