xen: implement CPU hotplugging

Note the changes from 2.6.18-xen CPU hotplugging:

A vcpu_down request from the remote admin via Xenbus both hotunplugs the
CPU, and disables it by removing it from the cpu_present map, and removing
its entry in /sys.

A vcpu_up request from the remote admin only re-enables the CPU, and does
not immediately bring the CPU up. A udev event is emitted, which can be
caught by the user if he wishes to automatically re-up CPUs when available,
or implement a more complex policy.

Signed-off-by: Alex Nixon <alex.nixon@citrix.com>
Acked-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 48 insertions, 12 deletions

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index baca7f2fbd8a..be5cbb2b7c60 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -11,8 +11,6 @@
  * useful topology information for the kernel to make use of.  As a
  * result, all CPUs are treated as if they're single-core and
  * single-threaded.
- *
- * This does not handle HOTPLUG_CPU yet.
  */
 #include <linux/sched.h>
 #include <linux/err.h>
@@ -61,11 +59,12 @@ static irqreturn_t xen_reschedule_interrupt(int irq, void *dev_id)
         return IRQ_HANDLED;
 }
 
-static __cpuinit void cpu_bringup_and_idle(void)
+static __cpuinit void cpu_bringup(void)
 {
         int cpu = smp_processor_id();
 
         cpu_init();
+        touch_softlockup_watchdog();
         preempt_disable();
 
         xen_enable_sysenter();
@@ -86,6 +85,11 @@ static __cpuinit void cpu_bringup_and_idle(void)
         local_irq_enable();
 
         wmb();                  /* make sure everything is out */
+}
+
+static __cpuinit void cpu_bringup_and_idle(void)
+{
+        cpu_bringup();
         cpu_idle();
 }
 
@@ -209,8 +213,6 @@ static void __init xen_smp_prepare_cpus(unsigned int max_cpus)
 
                 cpu_set(cpu, cpu_present_map);
         }
-
-        //init_xenbus_allowed_cpumask();
 }
 
 static __cpuinit int
@@ -278,12 +280,6 @@ static int __cpuinit xen_cpu_up(unsigned int cpu)
         struct task_struct *idle = idle_task(cpu);
         int rc;
 
-#if 0
-        rc = cpu_up_check(cpu);
-        if (rc)
-                return rc;
-#endif
-
 #ifdef CONFIG_X86_64
         /* Allocate node local memory for AP pdas */
         WARN_ON(cpu == 0);
@@ -336,6 +332,42 @@ static void xen_smp_cpus_done(unsigned int max_cpus)
 {
 }
 
+int xen_cpu_disable(void)
+{
+        unsigned int cpu = smp_processor_id();
+        if (cpu == 0)
+                return -EBUSY;
+
+        cpu_disable_common();
+
+        load_cr3(swapper_pg_dir);
+        return 0;
+}
+
+void xen_cpu_die(unsigned int cpu)
+{
+        while (HYPERVISOR_vcpu_op(VCPUOP_is_up, cpu, NULL)) {
+                current->state = TASK_UNINTERRUPTIBLE;
+                schedule_timeout(HZ/10);
+        }
+        unbind_from_irqhandler(per_cpu(resched_irq, cpu), NULL);
+        unbind_from_irqhandler(per_cpu(callfunc_irq, cpu), NULL);
+        unbind_from_irqhandler(per_cpu(debug_irq, cpu), NULL);
+        unbind_from_irqhandler(per_cpu(callfuncsingle_irq, cpu), NULL);
+        xen_uninit_lock_cpu(cpu);
+        xen_teardown_timer(cpu);
+
+        if (num_online_cpus() == 1)
+                alternatives_smp_switch(0);
+}
+
+void xen_play_dead(void)
+{
+        play_dead_common();
+        HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
+        cpu_bringup();
+}
+
 static void stop_self(void *v)
 {
         int cpu = smp_processor_id();
@@ -419,9 +451,13 @@ static irqreturn_t xen_call_function_single_interrupt(int irq, void *dev_id)
 static const struct smp_ops xen_smp_ops __initdata = {
         .smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu,
         .smp_prepare_cpus = xen_smp_prepare_cpus,
-        .cpu_up = xen_cpu_up,
         .smp_cpus_done = xen_smp_cpus_done,
 
+        .cpu_up = xen_cpu_up,
+        .cpu_die = xen_cpu_die,
+        .cpu_disable = xen_cpu_disable,
+        .play_dead = xen_play_dead,
+
         .smp_send_stop = xen_smp_send_stop,
         .smp_send_reschedule = xen_smp_send_reschedule,