[Xen-devel] [PATCH] xen: honour VCPU availability on boot

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
 drivers/xen/cpu_hotplug.c |   40 ++++++++++++++++++++++++++++++----------
 1 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/drivers/xen/cpu_hotplug.c b/drivers/xen/cpu_hotplug.c
index 974f56d..411cb1f 100644
--- a/drivers/xen/cpu_hotplug.c
+++ b/drivers/xen/cpu_hotplug.c
@@ -21,29 +21,41 @@ static void disable_hotplug_cpu(int cpu)
        cpu_clear(cpu, cpu_present_map);
 }
 
-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;
 }
 
-- 
1.5.6.5


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