xen: honour VCPU availability on boot

If a VM is booted with offline VCPUs then unplug them during boot. Determining
the availability of a VCPU requires access to XenStore which is not available
at the point smp_prepare_cpus() is called, therefore we bring up all VCPUS
initially and unplug the offline ones as soon as XenStore becomes available.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

1 files changed, 30 insertions, 10 deletions

diff --git a/drivers/xen/cpu_hotplug.c b/drivers/xen/cpu_hotplug.c
index 5f54c01c1568..bdfd584ad853 100644
--- a/drivers/xen/cpu_hotplug.c
+++ b/drivers/xen/cpu_hotplug.c
@@ -21,29 +21,41 @@ static void disable_hotplug_cpu(int cpu)
         set_cpu_present(cpu, false);
 }
 
-static void vcpu_hotplug(unsigned int cpu)
+static int vcpu_online(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;
+                return err;
         }
 
-        if (strcmp(state, "online") == 0) {
+        if (strcmp(state, "online") == 0)
+                return 1;
+        else if (strcmp(state, "offline") == 0)
+                return 0;
+
+        printk(KERN_ERR "XENBUS: unknown state(%s) on CPU%d\n", state, cpu);
+        return -EINVAL;
+}
+static void vcpu_hotplug(unsigned int cpu)
+{
+        if (!cpu_possible(cpu))
+                return;
+
+        switch (vcpu_online(cpu)) {
+        case 1:
                 enable_hotplug_cpu(cpu);
-        } else if (strcmp(state, "offline") == 0) {
+                break;
+        case 0:
                 (void)cpu_down(cpu);
                 disable_hotplug_cpu(cpu);
-        } else {
-                printk(KERN_ERR "XENBUS: unknown state(%s) on CPU%d\n",
-                       state, cpu);
+                break;
+        default:
+                break;
         }
 }
 
@@ -64,12 +76,20 @@ static void handle_vcpu_hotplug_event(struct xenbus_watch *watch,
 static int setup_cpu_watcher(struct notifier_block *notifier,
                               unsigned long event, void *data)
 {
+        int cpu;
         static struct xenbus_watch cpu_watch = {
                 .node = "cpu",
                 .callback = handle_vcpu_hotplug_event};
 
         (void)register_xenbus_watch(&cpu_watch);
 
+        for_each_possible_cpu(cpu) {
+                if (vcpu_online(cpu) == 0) {
+                        (void)cpu_down(cpu);
+                        cpu_clear(cpu, cpu_present_map);
+                }
+        }
+
         return NOTIFY_DONE;
 }