+static int wakeup_cpu0_nmi(unsigned int cmd, struct pt_regs *regs)
+{
+ int cpu;
+
+ cpu = smp_processor_id();
+ if (cpu == 0 && !cpu_online(cpu) && enable_start_cpu0)
+ return NMI_HANDLED;
+
+ return NMI_DONE;
+}
+
+/*
+ * Wake up AP by INIT, INIT, STARTUP sequence.
+ *
+ * Instead of waiting for STARTUP after INITs, BSP will execute the BIOS
+ * boot-strap code which is not a desired behavior for waking up BSP. To
+ * void the boot-strap code, wake up CPU0 by NMI instead.
+ *
+ * This works to wake up soft offlined CPU0 only. If CPU0 is hard offlined
+ * (i.e. physically hot removed and then hot added), NMI won't wake it up.
+ * We'll change this code in the future to wake up hard offlined CPU0 if
+ * real platform and request are available.
+ */
+static int __cpuinit
+wakeup_cpu_via_init_nmi(int cpu, unsigned long start_ip, int apicid,
+ int *cpu0_nmi_registered)
+{
+ int id;
+ int boot_error;
+
+ /*
+ * Wake up AP by INIT, INIT, STARTUP sequence.
+ */
+ if (cpu)
+ return wakeup_secondary_cpu_via_init(apicid, start_ip);
+
+ /*
+ * Wake up BSP by nmi.
+ *
+ * Register a NMI handler to help wake up CPU0.
+ */
+ boot_error = register_nmi_handler(NMI_LOCAL,
+ wakeup_cpu0_nmi, 0, "wake_cpu0");
+
+ if (!boot_error) {
+ enable_start_cpu0 = 1;
+ *cpu0_nmi_registered = 1;
+ if (apic->dest_logical == APIC_DEST_LOGICAL)
+ id = cpu0_logical_apicid;
+ else
+ id = apicid;
+ boot_error = wakeup_secondary_cpu_via_nmi(id, start_ip);
+ }
+
+ return boot_error;
+}
+