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, 90 insertions, 0 deletions

diff --git a/drivers/xen/cpu_hotplug.c b/drivers/xen/cpu_hotplug.c
new file mode 100644
index 000000000000..1bc003536cdb
--- /dev/null
+++ b/drivers/xen/cpu_hotplug.c
@@ -0,0 +1,90 @@
+#include <linux/notifier.h>
+
+#include <xen/xenbus.h>
+
+#include <asm-x86/xen/hypervisor.h>
+#include <asm/cpu.h>
+
+static void enable_hotplug_cpu(int cpu)
+{
+        if (!cpu_present(cpu))
+                arch_register_cpu(cpu);
+
+        cpu_set(cpu, cpu_present_map);
+}
+
+static void disable_hotplug_cpu(int cpu)
+{
+        if (cpu_present(cpu))
+                arch_unregister_cpu(cpu);
+
+        cpu_clear(cpu, cpu_present_map);
+}
+
+static void vcpu_hotplug(unsigned int cpu)
+{
+        int err;
+        char dir[32], state[32];
+
+        if (!cpu_possible(cpu))
+                return;
+
+        sprintf(dir, "cpu/%u", cpu);
+        err = xenbus_scanf(XBT_NIL, dir, "availability", "%s", state);
+        if (err != 1) {
+                printk(KERN_ERR "XENBUS: Unable to read cpu state\n");
+                return;
+        }
+
+        if (strcmp(state, "online") == 0) {
+                enable_hotplug_cpu(cpu);
+        } else if (strcmp(state, "offline") == 0) {
+                (void)cpu_down(cpu);
+                disable_hotplug_cpu(cpu);
+        } else {
+                printk(KERN_ERR "XENBUS: unknown state(%s) on CPU%d\n",
+                       state, cpu);
+        }
+}
+
+static void handle_vcpu_hotplug_event(struct xenbus_watch *watch,
+                                        const char **vec, unsigned int len)
+{
+        unsigned int cpu;
+        char *cpustr;
+        const char *node = vec[XS_WATCH_PATH];
+
+        cpustr = strstr(node, "cpu/");
+        if (cpustr != NULL) {
+                sscanf(cpustr, "cpu/%u", &cpu);
+                vcpu_hotplug(cpu);
+        }
+}
+
+static int setup_cpu_watcher(struct notifier_block *notifier,
+                              unsigned long event, void *data)
+{
+        static struct xenbus_watch cpu_watch = {
+                .node = "cpu",
+                .callback = handle_vcpu_hotplug_event};
+
+        (void)register_xenbus_watch(&cpu_watch);
+
+        return NOTIFY_DONE;
+}
+
+static int __init setup_vcpu_hotplug_event(void)
+{
+        static struct notifier_block xsn_cpu = {
+                .notifier_call = setup_cpu_watcher };
+
+        if (!is_running_on_xen())
+                return -ENODEV;
+
+        register_xenstore_notifier(&xsn_cpu);
+
+        return 0;
+}
+
+arch_initcall(setup_vcpu_hotplug_event);
+