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-rw-r--r--arch/x86/Kconfig15
-rw-r--r--arch/x86/include/asm/cpu.h3
-rw-r--r--arch/x86/kernel/topology.c51
-rw-r--r--arch/x86/power/cpu.c38
4 files changed, 107 insertions, 0 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 036e89ab470c..b6cfa5f62529 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1727,6 +1727,21 @@ config BOOTPARAM_HOTPLUG_CPU0
You still can enable the CPU0 hotplug feature at boot by kernel
parameter cpu0_hotplug.
+config DEBUG_HOTPLUG_CPU0
+ def_bool n
+ prompt "Debug CPU0 hotplug"
+ depends on HOTPLUG_CPU && EXPERIMENTAL
+ ---help---
+ Enabling this option offlines CPU0 (if CPU0 can be offlined) as
+ soon as possible and boots up userspace with CPU0 offlined. User
+ can online CPU0 back after boot time.
+
+ To debug CPU0 hotplug, you need to enable CPU0 offline/online
+ feature by either turning on CONFIG_BOOTPARAM_HOTPLUG_CPU0 during
+ compilation or giving cpu0_hotplug kernel parameter at boot.
+
+ If unsure, say N.
+
config COMPAT_VDSO
def_bool y
prompt "Compat VDSO support"
diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index a1195726e8c2..5f9a1243190e 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -29,6 +29,9 @@ struct x86_cpu {
extern int arch_register_cpu(int num);
extern void arch_unregister_cpu(int);
extern void __cpuinit start_cpu0(void);
+#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
+extern int _debug_hotplug_cpu(int cpu, int action);
+#endif
#endif
DECLARE_PER_CPU(int, cpu_state);
diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index 0e7b4a7a7fb8..6e60b5fe2244 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c
@@ -50,6 +50,57 @@ static int __init enable_cpu0_hotplug(char *str)
__setup("cpu0_hotplug", enable_cpu0_hotplug);
#endif
+#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
+/*
+ * This function offlines a CPU as early as possible and allows userspace to
+ * boot up without the CPU. The CPU can be onlined back by user after boot.
+ *
+ * This is only called for debugging CPU offline/online feature.
+ */
+int __ref _debug_hotplug_cpu(int cpu, int action)
+{
+ struct device *dev = get_cpu_device(cpu);
+ int ret;
+
+ if (!cpu_is_hotpluggable(cpu))
+ return -EINVAL;
+
+ cpu_hotplug_driver_lock();
+
+ switch (action) {
+ case 0:
+ ret = cpu_down(cpu);
+ if (!ret) {
+ pr_info("CPU %u is now offline\n", cpu);
+ kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
+ } else
+ pr_debug("Can't offline CPU%d.\n", cpu);
+ break;
+ case 1:
+ ret = cpu_up(cpu);
+ if (!ret)
+ kobject_uevent(&dev->kobj, KOBJ_ONLINE);
+ else
+ pr_debug("Can't online CPU%d.\n", cpu);
+ break;
+ default:
+ ret = -EINVAL;
+ }
+
+ cpu_hotplug_driver_unlock();
+
+ return ret;
+}
+
+static int __init debug_hotplug_cpu(void)
+{
+ _debug_hotplug_cpu(0, 0);
+ return 0;
+}
+
+late_initcall_sync(debug_hotplug_cpu);
+#endif /* CONFIG_DEBUG_HOTPLUG_CPU0 */
+
int __ref arch_register_cpu(int num)
{
struct cpuinfo_x86 *c = &cpu_data(num);
diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index adde77588e25..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;
@@ -263,6 +264,43 @@ static int bsp_pm_callback(struct notifier_block *nb, unsigned long action,
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;
}