Merge branch 'x86-bsp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 BSP hotplug changes from Ingo Molnar:
 "This tree enables CPU#0 (the boot processor) to be onlined/offlined on
  x86, just like any other CPU.  Enabled on Intel CPUs for now.

  Allowing this required the identification and fixing of latent CPU#0
  assumptions (such as CPU#0 initializations, etc.) in the x86
  architecture code, plus the identification of barriers to
  BSP-offlining, such as active PIC interrupts which can only be
  serviced on the BSP.

  It's behind a default-off option, and there's a debug option that
  allows the automatic testing of this feature.

  The motivation of this feature is to allow and prepare for true
  CPU-hotplug hardware support: recent changes to MCE support enable us
  to detect a deteriorating but not yet hard-failing L1/L2 cache on a
  CPU that could be soft-unplugged - or a failing L3 cache on a
  multi-socket system.

  Note that true hardware hot-plug is not yet fully enabled by this,
  because that requires a special platform wakeup sequence to be sent to
  the freshly powered up CPU#0.  Future patches for this are planned,
  once such a platform exists.  Chicken and egg"

* 'x86-bsp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86, topology: Debug CPU0 hotplug
  x86/i387.c: Initialize thread xstate only on CPU0 only once
  x86, hotplug: Handle retrigger irq by the first available CPU
  x86, hotplug: The first online processor saves the MTRR state
  x86, hotplug: During CPU0 online, enable x2apic, set_numa_node.
  x86, hotplug: Wake up CPU0 via NMI instead of INIT, SIPI, SIPI
  x86-32, hotplug: Add start_cpu0() entry point to head_32.S
  x86-64, hotplug: Add start_cpu0() entry point to head_64.S
  kernel/cpu.c: Add comment for priority in cpu_hotplug_pm_callback
  x86, hotplug, suspend: Online CPU0 for suspend or hibernate
  x86, hotplug: Support functions for CPU0 online/offline
  x86, topology: Don't offline CPU0 if any PIC irq can not be migrated out of it
  x86, Kconfig: Add config switch for CPU0 hotplug
  doc: Add x86 CPU0 online/offline feature

arch/x86/kernel/smpboot.c

@@ -127,8 +127,8 @@ EXPORT_PER_CPU_SYMBOL(cpu_info);
 atomic_t init_deasserted;
 
 /*
- * Report back to the Boot Processor.
- * Running on AP.
+ * Report back to the Boot Processor during boot time or to the caller processor
+ * during CPU online.
  */
 static void __cpuinit smp_callin(void)
 {
@@ -140,15 +140,17 @@ static void __cpuinit smp_callin(void)
 	 * we may get here before an INIT-deassert IPI reaches
 	 * our local APIC.  We have to wait for the IPI or we'll
 	 * lock up on an APIC access.
+	 *
+	 * Since CPU0 is not wakened up by INIT, it doesn't wait for the IPI.
 	 */
-	if (apic->wait_for_init_deassert)
+	cpuid = smp_processor_id();
+	if (apic->wait_for_init_deassert && cpuid != 0)
 		apic->wait_for_init_deassert(&init_deasserted);
 
 	/*
 	 * (This works even if the APIC is not enabled.)
 	 */
 	phys_id = read_apic_id();
-	cpuid = smp_processor_id();
 	if (cpumask_test_cpu(cpuid, cpu_callin_mask)) {
 		panic("%s: phys CPU#%d, CPU#%d already present??\n", __func__,
 					phys_id, cpuid);
@@ -230,6 +232,8 @@ static void __cpuinit smp_callin(void)
 	cpumask_set_cpu(cpuid, cpu_callin_mask);
 }
 
+static int cpu0_logical_apicid;
+static int enable_start_cpu0;
 /*
  * Activate a secondary processor.
  */
@@ -245,6 +249,8 @@ notrace static void __cpuinit start_secondary(void *unused)
 	preempt_disable();
 	smp_callin();
 
+	enable_start_cpu0 = 0;
+
 #ifdef CONFIG_X86_32
 	/* switch away from the initial page table */
 	load_cr3(swapper_pg_dir);
@@ -281,19 +287,30 @@ notrace static void __cpuinit start_secondary(void *unused)
 	cpu_idle();
 }
 
+void __init smp_store_boot_cpu_info(void)
+{
+	int id = 0; /* CPU 0 */
+	struct cpuinfo_x86 *c = &cpu_data(id);
+
+	*c = boot_cpu_data;
+	c->cpu_index = id;
+}
+
 /*
  * The bootstrap kernel entry code has set these up. Save them for
  * a given CPU
  */
-
 void __cpuinit smp_store_cpu_info(int id)
 {
 	struct cpuinfo_x86 *c = &cpu_data(id);
 
 	*c = boot_cpu_data;
 	c->cpu_index = id;
-	if (id != 0)
-		identify_secondary_cpu(c);
+	/*
+	 * During boot time, CPU0 has this setup already. Save the info when
+	 * bringing up AP or offlined CPU0.
+	 */
+	identify_secondary_cpu(c);
 }
 
 static bool __cpuinit
@@ -483,7 +500,7 @@ void __inquire_remote_apic(int apicid)
  * won't ... remember to clear down the APIC, etc later.
  */
 int __cpuinit
-wakeup_secondary_cpu_via_nmi(int logical_apicid, unsigned long start_eip)
+wakeup_secondary_cpu_via_nmi(int apicid, unsigned long start_eip)
 {
 	unsigned long send_status, accept_status = 0;
 	int maxlvt;
@@ -491,7 +508,7 @@ wakeup_secondary_cpu_via_nmi(int logical_apicid, unsigned long start_eip)
 	/* Target chip */
 	/* Boot on the stack */
 	/* Kick the second */
-	apic_icr_write(APIC_DM_NMI | apic->dest_logical, logical_apicid);
+	apic_icr_write(APIC_DM_NMI | apic->dest_logical, apicid);
 
 	pr_debug("Waiting for send to finish...\n");
 	send_status = safe_apic_wait_icr_idle();
@@ -651,6 +668,63 @@ static void __cpuinit announce_cpu(int cpu, int apicid)
 			node, cpu, apicid);
 }
 
+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;
+}
+
 /*
  * NOTE - on most systems this is a PHYSICAL apic ID, but on multiquad
  * (ie clustered apic addressing mode), this is a LOGICAL apic ID.
@@ -666,6 +740,7 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
 
 	unsigned long boot_error = 0;
 	int timeout;
+	int cpu0_nmi_registered = 0;
 
 	/* Just in case we booted with a single CPU. */
 	alternatives_enable_smp();
@@ -713,13 +788,16 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
 	}
 
 	/*
-	 * Kick the secondary CPU. Use the method in the APIC driver
-	 * if it's defined - or use an INIT boot APIC message otherwise:
+	 * Wake up a CPU in difference cases:
+	 * - Use the method in the APIC driver if it's defined
+	 * Otherwise,
+	 * - Use an INIT boot APIC message for APs or NMI for BSP.
 	 */
 	if (apic->wakeup_secondary_cpu)
 		boot_error = apic->wakeup_secondary_cpu(apicid, start_ip);
 	else
-		boot_error = wakeup_secondary_cpu_via_init(apicid, start_ip);
+		boot_error = wakeup_cpu_via_init_nmi(cpu, start_ip, apicid,
+						     &cpu0_nmi_registered);
 
 	if (!boot_error) {
 		/*
@@ -784,6 +862,13 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
 		 */
 		smpboot_restore_warm_reset_vector();
 	}
+	/*
+	 * Clean up the nmi handler. Do this after the callin and callout sync
+	 * to avoid impact of possible long unregister time.
+	 */
+	if (cpu0_nmi_registered)
+		unregister_nmi_handler(NMI_LOCAL, "wake_cpu0");
+
 	return boot_error;
 }
 
@@ -797,7 +882,7 @@ int __cpuinit native_cpu_up(unsigned int cpu, struct task_struct *tidle)
 
 	pr_debug("++++++++++++++++++++=_---CPU UP  %u\n", cpu);
 
-	if (apicid == BAD_APICID || apicid == boot_cpu_physical_apicid ||
+	if (apicid == BAD_APICID ||
 	    !physid_isset(apicid, phys_cpu_present_map) ||
 	    !apic->apic_id_valid(apicid)) {
 		pr_err("%s: bad cpu %d\n", __func__, cpu);
@@ -995,7 +1080,7 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 	/*
 	 * Setup boot CPU information
 	 */
-	smp_store_cpu_info(0); /* Final full version of the data */
+	smp_store_boot_cpu_info(); /* Final full version of the data */
 	cpumask_copy(cpu_callin_mask, cpumask_of(0));
 	mb();
 
@@ -1031,6 +1116,11 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 	 */
 	setup_local_APIC();
 
+	if (x2apic_mode)
+		cpu0_logical_apicid = apic_read(APIC_LDR);
+	else
+		cpu0_logical_apicid = GET_APIC_LOGICAL_ID(apic_read(APIC_LDR));
+
 	/*
 	 * Enable IO APIC before setting up error vector
 	 */
@@ -1219,19 +1309,6 @@ void cpu_disable_common(void)
 
 int native_cpu_disable(void)
 {
-	int cpu = smp_processor_id();
-
-	/*
-	 * Perhaps use cpufreq to drop frequency, but that could go
-	 * into generic code.
-	 *
-	 * We won't take down the boot processor on i386 due to some
-	 * interrupts only being able to be serviced by the BSP.
-	 * Especially so if we're not using an IOAPIC	-zwane
-	 */
-	if (cpu == 0)
-		return -EBUSY;
-
 	clear_local_APIC();
 
 	cpu_disable_common();
@@ -1271,6 +1348,14 @@ void play_dead_common(void)
 	local_irq_disable();
 }
 
+static bool wakeup_cpu0(void)
+{
+	if (smp_processor_id() == 0 && enable_start_cpu0)
+		return true;
+
+	return false;
+}
+
 /*
  * We need to flush the caches before going to sleep, lest we have
  * dirty data in our caches when we come back up.
@@ -1334,6 +1419,11 @@ static inline void mwait_play_dead(void)
 		__monitor(mwait_ptr, 0, 0);
 		mb();
 		__mwait(eax, 0);
+		/*
+		 * If NMI wants to wake up CPU0, start CPU0.
+		 */
+		if (wakeup_cpu0())
+			start_cpu0();
 	}
 }
 
@@ -1344,6 +1434,11 @@ static inline void hlt_play_dead(void)
 
 	while (1) {
 		native_halt();
+		/*
+		 * If NMI wants to wake up CPU0, start CPU0.
+		 */
+		if (wakeup_cpu0())
+			start_cpu0();
 	}
 }