[PATCH] x86_64: CPU hotplug support

  Experimental CPU hotplug patch for x86_64
  -----------------------------------------
This supports logical CPU online and offline.
- Test with maxcpus=1, and then kick other cpu's off to test if init code
  is all cleaned up. CONFIG_SCHED_SMT works as well.
- idle threads are forked on demand from keventd threads for clean startup

TBD:
1. Not tested on a real NUMA machine (tested with numa=fake=2)
2. Handle ACPI pieces for physical hotplug support.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Acked-by: Andi Kleen <ak@muc.de>
Acked-by: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Signed-off-by: Shaohua.li<shaohua.li@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

5 files changed, 263 insertions, 17 deletions

diff --git a/arch/x86_64/Kconfig b/arch/x86_64/Kconfig
index db259757dc8a..92f5a5266023 100644
--- a/arch/x86_64/Kconfig
+++ b/arch/x86_64/Kconfig
@@ -313,6 +313,15 @@ config NR_CPUS
           This is purely to save memory - each supported CPU requires
           memory in the static kernel configuration.
 
+config HOTPLUG_CPU
+        bool "Support for hot-pluggable CPUs (EXPERIMENTAL)"
+        depends on SMP && HOTPLUG && EXPERIMENTAL
+        help
+                Say Y here to experiment with turning CPUs off and on.  CPUs
+                can be controlled through /sys/devices/system/cpu/cpu#.
+                Say N if you want to disable CPU hotplug.
+
+
 config HPET_TIMER
         bool
         default y
diff --git a/arch/x86_64/kernel/irq.c b/arch/x86_64/kernel/irq.c
index 62b112e4deb4..cc3fb85f5145 100644
--- a/arch/x86_64/kernel/irq.c
+++ b/arch/x86_64/kernel/irq.c
@@ -14,6 +14,7 @@
 #include <linux/interrupt.h>
 #include <linux/seq_file.h>
 #include <linux/module.h>
+#include <linux/delay.h>
 #include <asm/uaccess.h>
 #include <asm/io_apic.h>
 
@@ -106,3 +107,31 @@ asmlinkage unsigned int do_IRQ(struct pt_regs *regs)
         return 1;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+void fixup_irqs(cpumask_t map)
+{
+        unsigned int irq;
+        static int warned;
+
+        for (irq = 0; irq < NR_IRQS; irq++) {
+                cpumask_t mask;
+                if (irq == 2)
+                        continue;
+
+                cpus_and(mask, irq_affinity[irq], map);
+                if (any_online_cpu(mask) == NR_CPUS) {
+                        printk("Breaking affinity for irq %i\n", irq);
+                        mask = map;
+                }
+                if (irq_desc[irq].handler->set_affinity)
+                        irq_desc[irq].handler->set_affinity(irq, mask);
+                else if (irq_desc[irq].action && !(warned++))
+                        printk("Cannot set affinity for irq %i\n", irq);
+        }
+
+        /* That doesn't seem sufficient.  Give it 1ms. */
+        local_irq_enable();
+        mdelay(1);
+        local_irq_disable();
+}
+#endif
diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index 15fa35a81a72..1d91271796e5 100644
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -8,7 +8,8 @@
  * 
  *  X86-64 port
  *      Andi Kleen.
- * 
+ *
+ *      CPU hotplug support - ashok.raj@intel.com
  *  $Id: process.c,v 1.38 2002/01/15 10:08:03 ak Exp $
  */
 
@@ -18,6 +19,7 @@
 
 #include <stdarg.h>
 
+#include <linux/cpu.h>
 #include <linux/errno.h>
 #include <linux/sched.h>
 #include <linux/kernel.h>
@@ -154,6 +156,29 @@ void cpu_idle_wait(void)
 }
 EXPORT_SYMBOL_GPL(cpu_idle_wait);
 
+#ifdef CONFIG_HOTPLUG_CPU
+DECLARE_PER_CPU(int, cpu_state);
+
+#include <asm/nmi.h>
+/* We don't actually take CPU down, just spin without interrupts. */
+static inline void play_dead(void)
+{
+        idle_task_exit();
+        wbinvd();
+        mb();
+        /* Ack it */
+        __get_cpu_var(cpu_state) = CPU_DEAD;
+
+        while (1)
+                safe_halt();
+}
+#else
+static inline void play_dead(void)
+{
+        BUG();
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
 /*
  * The idle thread. There's no useful work to be
  * done, so just try to conserve power and have a
@@ -174,6 +199,8 @@ void cpu_idle (void)
                         idle = pm_idle;
                         if (!idle)
                                 idle = default_idle;
+                        if (cpu_is_offline(smp_processor_id()))
+                                play_dead();
                         idle();
                 }
 
diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c
index bc98a6722cba..5a3f955b6576 100644
--- a/arch/x86_64/kernel/smpboot.c
+++ b/arch/x86_64/kernel/smpboot.c
@@ -34,6 +34,7 @@
  *      Andi Kleen              :       Converted to new state machine.
  *                                      Various cleanups.
  *                                      Probably mostly hotplug CPU ready now.
+ *      Ashok Raj                       : CPU hotplug support
  */
 
 
@@ -98,6 +99,37 @@ EXPORT_SYMBOL(cpu_core_map);
 extern unsigned char trampoline_data[];
 extern unsigned char trampoline_end[];
 
+/* State of each CPU */
+DEFINE_PER_CPU(int, cpu_state) = { 0 };
+
+/*
+ * Store all idle threads, this can be reused instead of creating
+ * a new thread. Also avoids complicated thread destroy functionality
+ * for idle threads.
+ */
+struct task_struct *idle_thread_array[NR_CPUS] __cpuinitdata ;
+
+#define get_idle_for_cpu(x)     (idle_thread_array[(x)])
+#define set_idle_for_cpu(x,p)   (idle_thread_array[(x)] = (p))
+
+/*
+ * cpu_possible_map should be static, it cannot change as cpu's
+ * are onlined, or offlined. The reason is per-cpu data-structures
+ * are allocated by some modules at init time, and dont expect to
+ * do this dynamically on cpu arrival/departure.
+ * cpu_present_map on the other hand can change dynamically.
+ * In case when cpu_hotplug is not compiled, then we resort to current
+ * behaviour, which is cpu_possible == cpu_present.
+ * If cpu-hotplug is supported, then we need to preallocate for all
+ * those NR_CPUS, hence cpu_possible_map represents entire NR_CPUS range.
+ * - Ashok Raj
+ */
+#ifdef CONFIG_HOTPLUG_CPU
+#define fixup_cpu_possible_map(x)       cpu_set((x), cpu_possible_map)
+#else
+#define fixup_cpu_possible_map(x)
+#endif
+
 /*
  * Currently trivial. Write the real->protected mode
  * bootstrap into the page concerned. The caller
@@ -623,33 +655,77 @@ static int __cpuinit wakeup_secondary_via_INIT(int phys_apicid, unsigned int sta
         return (send_status | accept_status);
 }
 
+struct create_idle {
+        struct task_struct *idle;
+        struct completion done;
+        int cpu;
+};
+
+void do_fork_idle(void *_c_idle)
+{
+        struct create_idle *c_idle = _c_idle;
+
+        c_idle->idle = fork_idle(c_idle->cpu);
+        complete(&c_idle->done);
+}
+
 /*
  * Boot one CPU.
  */
 static int __cpuinit do_boot_cpu(int cpu, int apicid)
 {
-        struct task_struct *idle;
         unsigned long boot_error;
         int timeout;
         unsigned long start_rip;
+        struct create_idle c_idle = {
+                .cpu = cpu,
+                .done = COMPLETION_INITIALIZER(c_idle.done),
+        };
+        DECLARE_WORK(work, do_fork_idle, &c_idle);
+
+        c_idle.idle = get_idle_for_cpu(cpu);
+
+        if (c_idle.idle) {
+                c_idle.idle->thread.rsp = (unsigned long) (((struct pt_regs *)
+                        (THREAD_SIZE + (unsigned long) c_idle.idle->thread_info)) - 1);
+                init_idle(c_idle.idle, cpu);
+                goto do_rest;
+        }
+
         /*
-         * We can't use kernel_thread since we must avoid to
-         * reschedule the child.
+         * During cold boot process, keventd thread is not spun up yet.
+         * When we do cpu hot-add, we create idle threads on the fly, we should
+         * not acquire any attributes from the calling context. Hence the clean
+         * way to create kernel_threads() is to do that from keventd().
+         * We do the current_is_keventd() due to the fact that ACPI notifier
+         * was also queuing to keventd() and when the caller is already running
+         * in context of keventd(), we would end up with locking up the keventd
+         * thread.
          */
-        idle = fork_idle(cpu);
-        if (IS_ERR(idle)) {
+        if (!keventd_up() || current_is_keventd())
+                work.func(work.data);
+        else {
+                schedule_work(&work);
+                wait_for_completion(&c_idle.done);
+        }
+
+        if (IS_ERR(c_idle.idle)) {
                 printk("failed fork for CPU %d\n", cpu);
-                return PTR_ERR(idle);
+                return PTR_ERR(c_idle.idle);
         }
 
-        cpu_pda[cpu].pcurrent = idle;
+        set_idle_for_cpu(cpu, c_idle.idle);
+
+do_rest:
+
+        cpu_pda[cpu].pcurrent = c_idle.idle;
 
         start_rip = setup_trampoline();
 
-        init_rsp = idle->thread.rsp;
+        init_rsp = c_idle.idle->thread.rsp;
         per_cpu(init_tss,cpu).rsp0 = init_rsp;
         initial_code = start_secondary;
-        clear_ti_thread_flag(idle->thread_info, TIF_FORK);
+        clear_ti_thread_flag(c_idle.idle->thread_info, TIF_FORK);
 
         printk(KERN_INFO "Booting processor %d/%d rip %lx rsp %lx\n", cpu, apicid,
                start_rip, init_rsp);
@@ -925,10 +1001,9 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
                 int apicid = cpu_present_to_apicid(i);
                 if (physid_isset(apicid, phys_cpu_present_map)) {
                         cpu_set(i, cpu_present_map);
-                        /* possible map would be different if we supported real
-                           CPU hotplug. */
                         cpu_set(i, cpu_possible_map);
                 }
+                fixup_cpu_possible_map(i);
         }
 
         if (smp_sanity_check(max_cpus) < 0) {
@@ -977,9 +1052,6 @@ void __init smp_prepare_boot_cpu(void)
 
 /*
  * Entry point to boot a CPU.
- *
- * This is all __cpuinit, not __devinit for now because we don't support
- * CPU hotplug (yet).
  */
 int __cpuinit __cpu_up(unsigned int cpu)
 {
@@ -996,6 +1068,14 @@ int __cpuinit __cpu_up(unsigned int cpu)
                 return -EINVAL;
         }
 
+        /*
+         * Already booted CPU?
+         */
+        if (cpu_isset(cpu, cpu_callin_map)) {
+                Dprintk("do_boot_cpu %d Already started\n", cpu);
+                return -ENOSYS;
+        }
+
         /* Boot it! */
         err = do_boot_cpu(cpu, apicid);
         if (err < 0) {
@@ -1008,7 +1088,9 @@ int __cpuinit __cpu_up(unsigned int cpu)
 
         while (!cpu_isset(cpu, cpu_online_map))
                 cpu_relax();
-        return 0;
+        err = 0;
+
+        return err;
 }
 
 /*
@@ -1016,7 +1098,9 @@ int __cpuinit __cpu_up(unsigned int cpu)
  */
 void __init smp_cpus_done(unsigned int max_cpus)
 {
+#ifndef CONFIG_HOTPLUG_CPU
         zap_low_mappings();
+#endif
         smp_cleanup_boot();
 
 #ifdef CONFIG_X86_IO_APIC
@@ -1028,3 +1112,94 @@ void __init smp_cpus_done(unsigned int max_cpus)
 
         check_nmi_watchdog();
 }
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+static void
+remove_siblinginfo(int cpu)
+{
+        int sibling;
+
+        for_each_cpu_mask(sibling, cpu_sibling_map[cpu])
+                cpu_clear(cpu, cpu_sibling_map[sibling]);
+        for_each_cpu_mask(sibling, cpu_core_map[cpu])
+                cpu_clear(cpu, cpu_core_map[sibling]);
+        cpus_clear(cpu_sibling_map[cpu]);
+        cpus_clear(cpu_core_map[cpu]);
+        phys_proc_id[cpu] = BAD_APICID;
+        cpu_core_id[cpu] = BAD_APICID;
+}
+
+void remove_cpu_from_maps(void)
+{
+        int cpu = smp_processor_id();
+
+        cpu_clear(cpu, cpu_callout_map);
+        cpu_clear(cpu, cpu_callin_map);
+        clear_bit(cpu, &cpu_initialized); /* was set by cpu_init() */
+}
+
+int __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;
+
+        disable_APIC_timer();
+
+        /*
+         * HACK:
+         * Allow any queued timer interrupts to get serviced
+         * This is only a temporary solution until we cleanup
+         * fixup_irqs as we do for IA64.
+         */
+        local_irq_enable();
+        mdelay(1);
+
+        local_irq_disable();
+        remove_siblinginfo(cpu);
+
+        /* It's now safe to remove this processor from the online map */
+        cpu_clear(cpu, cpu_online_map);
+        remove_cpu_from_maps();
+        fixup_irqs(cpu_online_map);
+        return 0;
+}
+
+void __cpu_die(unsigned int cpu)
+{
+        /* We don't do anything here: idle task is faking death itself. */
+        unsigned int i;
+
+        for (i = 0; i < 10; i++) {
+                /* They ack this in play_dead by setting CPU_DEAD */
+                if (per_cpu(cpu_state, cpu) == CPU_DEAD)
+                        return;
+                current->state = TASK_UNINTERRUPTIBLE;
+                schedule_timeout(HZ/10);
+        }
+        printk(KERN_ERR "CPU %u didn't die...\n", cpu);
+}
+
+#else /* ... !CONFIG_HOTPLUG_CPU */
+
+int __cpu_disable(void)
+{
+        return -ENOSYS;
+}
+
+void __cpu_die(unsigned int cpu)
+{
+        /* We said "no" in __cpu_disable */
+        BUG();
+}
+#endif /* CONFIG_HOTPLUG_CPU */
diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index 121646fc43f6..102736630002 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -586,11 +586,17 @@ static void unknown_nmi_error(unsigned char reason, struct pt_regs * regs)
 asmlinkage void default_do_nmi(struct pt_regs *regs)
 {
         unsigned char reason = 0;
+        int cpu;
+
+        cpu = smp_processor_id();
 
         /* Only the BSP gets external NMIs from the system.  */
-        if (!smp_processor_id())
+        if (!cpu)
                 reason = get_nmi_reason();
 
+        if (!cpu_online(cpu))
+                return;
+
         if (!(reason & 0xc0)) {
                 if (notify_die(DIE_NMI_IPI, "nmi_ipi", regs, reason, 0, SIGINT)
                                                                 == NOTIFY_STOP)