1 files changed, 64 insertions, 0 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index a6cd1c1fe29a..291d298868fc 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -34,6 +34,7 @@
 #include <linux/highmem.h>
 #include <linux/file.h>
 #include <asm/desc.h>
+#include <linux/cpu.h>
 
 #include "x86_emulate.h"
 #include "segment_descriptor.h"
@@ -2039,6 +2040,64 @@ static struct notifier_block kvm_reboot_notifier = {
         .priority = 0,
 };
 
+/*
+ * Make sure that a cpu that is being hot-unplugged does not have any vcpus
+ * cached on it.
+ */
+static void decache_vcpus_on_cpu(int cpu)
+{
+        struct kvm *vm;
+        struct kvm_vcpu *vcpu;
+        int i;
+
+        spin_lock(&kvm_lock);
+        list_for_each_entry(vm, &vm_list, vm_list)
+                for (i = 0; i < KVM_MAX_VCPUS; ++i) {
+                        vcpu = &vm->vcpus[i];
+                        /*
+                         * If the vcpu is locked, then it is running on some
+                         * other cpu and therefore it is not cached on the
+                         * cpu in question.
+                         *
+                         * If it's not locked, check the last cpu it executed
+                         * on.
+                         */
+                        if (mutex_trylock(&vcpu->mutex)) {
+                                if (vcpu->cpu == cpu) {
+                                        kvm_arch_ops->vcpu_decache(vcpu);
+                                        vcpu->cpu = -1;
+                                }
+                                mutex_unlock(&vcpu->mutex);
+                        }
+                }
+        spin_unlock(&kvm_lock);
+}
+
+static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
+                           void *v)
+{
+        int cpu = (long)v;
+
+        switch (val) {
+        case CPU_DEAD:
+        case CPU_UP_CANCELED:
+                decache_vcpus_on_cpu(cpu);
+                smp_call_function_single(cpu, kvm_arch_ops->hardware_disable,
+                                         NULL, 0, 1);
+                break;
+        case CPU_UP_PREPARE:
+                smp_call_function_single(cpu, kvm_arch_ops->hardware_enable,
+                                         NULL, 0, 1);
+                break;
+        }
+        return NOTIFY_OK;
+}
+
+static struct notifier_block kvm_cpu_notifier = {
+        .notifier_call = kvm_cpu_hotplug,
+        .priority = 20, /* must be > scheduler priority */
+};
+
 static __init void kvm_init_debug(void)
 {
         struct kvm_stats_debugfs_item *p;
@@ -2085,6 +2144,9 @@ int kvm_init_arch(struct kvm_arch_ops *ops, struct module *module)
             return r;
 
         on_each_cpu(kvm_arch_ops->hardware_enable, NULL, 0, 1);
+        r = register_cpu_notifier(&kvm_cpu_notifier);
+        if (r)
+                goto out_free_1;
         register_reboot_notifier(&kvm_reboot_notifier);
 
         kvm_chardev_ops.owner = module;
@@ -2099,6 +2161,8 @@ int kvm_init_arch(struct kvm_arch_ops *ops, struct module *module)
 
 out_free:
         unregister_reboot_notifier(&kvm_reboot_notifier);
+        unregister_cpu_notifier(&kvm_cpu_notifier);
+out_free_1:
         on_each_cpu(kvm_arch_ops->hardware_disable, NULL, 0, 1);
         kvm_arch_ops->hardware_unsetup();
         return r;