x86: Skip cpus with apic-ids >= 255 in !x2apic_mode

If the x2apic mode is disabled for reasons like interrupt-remapping
not available etc, then we need to skip the logical cpu bringup of
apic-id's >= 255. Otherwise as the platform is in xapic mode, init/startup
IPI's will consider only the low 8-bits and there is a possibility of
re-sending init/startup IPI's to the logical cpu that is already online.

This will avoid potential reboots/unpredictable behavior etc.
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/20111222014632.702932458@sbsiddha-desk.sc.intel.comSigned-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/kernel/smpboot.c

@@ -840,7 +840,8 @@ int __cpuinit native_cpu_up(unsigned int cpu)
 	pr_debug("++++++++++++++++++++=_---CPU UP  %u\n", cpu);
 
 	if (apicid == BAD_APICID || apicid == boot_cpu_physical_apicid ||
-	    !physid_isset(apicid, phys_cpu_present_map)) {
+	    !physid_isset(apicid, phys_cpu_present_map) ||
+	    (!x2apic_mode && apicid >= 255)) {
 		printk(KERN_ERR "%s: bad cpu %d\n", __func__, cpu);
 		return -EINVAL;
 	}