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

1 files changed, 82 insertions, 0 deletions

diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index 218cdb16163c..120cee1c3f8d 100644
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -21,6 +21,7 @@
 #include <asm/suspend.h>
 #include <asm/debugreg.h>
 #include <asm/fpu-internal.h> /* pcntxt_mask */
+#include <asm/cpu.h>
 
 #ifdef CONFIG_X86_32
 static struct saved_context saved_context;
@@ -237,3 +238,84 @@ void restore_processor_state(void)
 #ifdef CONFIG_X86_32
 EXPORT_SYMBOL(restore_processor_state);
 #endif
+
+/*
+ * When bsp_check() is called in hibernate and suspend, cpu hotplug
+ * is disabled already. So it's unnessary to handle race condition between
+ * cpumask query and cpu hotplug.
+ */
+static int bsp_check(void)
+{
+	if (cpumask_first(cpu_online_mask) != 0) {
+		pr_warn("CPU0 is offline.\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+static int bsp_pm_callback(struct notifier_block *nb, unsigned long action,
+			   void *ptr)
+{
+	int ret = 0;
+
+	switch (action) {
+	case PM_SUSPEND_PREPARE:
+	case PM_HIBERNATION_PREPARE:
+		ret = bsp_check();
+		break;
+#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
+	case PM_RESTORE_PREPARE:
+		/*
+		 * When system resumes from hibernation, online CPU0 because
+		 * 1. it's required for resume and
+		 * 2. the CPU was online before hibernation
+		 */
+		if (!cpu_online(0))
+			_debug_hotplug_cpu(0, 1);
+		break;
+	case PM_POST_RESTORE:
+		/*
+		 * When a resume really happens, this code won't be called.
+		 *
+		 * This code is called only when user space hibernation software
+		 * prepares for snapshot device during boot time. So we just
+		 * call _debug_hotplug_cpu() to restore to CPU0's state prior to
+		 * preparing the snapshot device.
+		 *
+		 * This works for normal boot case in our CPU0 hotplug debug
+		 * mode, i.e. CPU0 is offline and user mode hibernation
+		 * software initializes during boot time.
+		 *
+		 * If CPU0 is online and user application accesses snapshot
+		 * device after boot time, this will offline CPU0 and user may
+		 * see different CPU0 state before and after accessing
+		 * the snapshot device. But hopefully this is not a case when
+		 * user debugging CPU0 hotplug. Even if users hit this case,
+		 * they can easily online CPU0 back.
+		 *
+		 * To simplify this debug code, we only consider normal boot
+		 * case. Otherwise we need to remember CPU0's state and restore
+		 * to that state and resolve racy conditions etc.
+		 */
+		_debug_hotplug_cpu(0, 0);
+		break;
+#endif
+	default:
+		break;
+	}
+	return notifier_from_errno(ret);
+}
+
+static int __init bsp_pm_check_init(void)
+{
+	/*
+	 * Set this bsp_pm_callback as lower priority than
+	 * cpu_hotplug_pm_callback. So cpu_hotplug_pm_callback will be called
+	 * earlier to disable cpu hotplug before bsp online check.
+	 */
+	pm_notifier(bsp_pm_callback, -INT_MAX);
+	return 0;
+}
+
+core_initcall(bsp_pm_check_init);