hi,

on monocpu machine (and maybe even on smp machine), when you try to 
acces to a cpu that don't exist (/dev/cpu/1/cpuid), cpuid (msr) call 
cpu_online, but on nosmp machine if the cpu!=0 this procude a BUG();
So I add a check that verify if the cpu can exist before calling cpu_online.

Matthieu CASTET