[PATCH] KVM: cpu hotplug support

On hotplug, we execute the hardware extension enable sequence.  On unplug, we
decache any vcpus that last ran on the exiting cpu, and execute the hardware
extension disable sequence.

Signed-off-by: Avi Kivity <avi@qumranet.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 64 insertions, 0 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index a6cd1c1..291d298 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;