KVM: Fix racy in kvm_free_assigned_irq
In the past, kvm_get_kvm() and kvm_put_kvm() was called in assigned device irq
handler and interrupt_work, in order to prevent cancel_work_sync() in
kvm_free_assigned_irq got a illegal state when waiting for interrupt_work done.
But it's tricky and still got two problems:
1. A bug ignored two conditions that cancel_work_sync() would return true result
in a additional kvm_put_kvm().
2. If interrupt type is MSI, we would got a window between cancel_work_sync()
and free_irq(), which interrupt would be injected again...
This patch discard the reference count used for irq handler and interrupt_work,
and ensure the legal state by moving the free function at the very beginning of
kvm_destroy_vm(). And the patch fix the second bug by disable irq before
cancel_work_sync(), which may result in nested disable of irq but OK for we are
going to free it.
Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b0fc079..fc3e329 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4129,11 +4129,11 @@
void kvm_arch_sync_events(struct kvm *kvm)
{
+ kvm_free_all_assigned_devices(kvm);
}
void kvm_arch_destroy_vm(struct kvm *kvm)
{
- kvm_free_all_assigned_devices(kvm);
kvm_iommu_unmap_guest(kvm);
kvm_free_pit(kvm);
kfree(kvm->arch.vpic);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 68e3f1e..277ea7f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -173,7 +173,6 @@
assigned_dev->host_irq_disabled = false;
}
mutex_unlock(&assigned_dev->kvm->lock);
- kvm_put_kvm(assigned_dev->kvm);
}
static irqreturn_t kvm_assigned_dev_intr(int irq, void *dev_id)
@@ -181,8 +180,6 @@
struct kvm_assigned_dev_kernel *assigned_dev =
(struct kvm_assigned_dev_kernel *) dev_id;
- kvm_get_kvm(assigned_dev->kvm);
-
schedule_work(&assigned_dev->interrupt_work);
disable_irq_nosync(irq);
@@ -213,6 +210,7 @@
}
}
+/* The function implicit hold kvm->lock mutex due to cancel_work_sync() */
static void kvm_free_assigned_irq(struct kvm *kvm,
struct kvm_assigned_dev_kernel *assigned_dev)
{
@@ -228,11 +226,24 @@
if (!assigned_dev->irq_requested_type)
return;
- if (cancel_work_sync(&assigned_dev->interrupt_work))
- /* We had pending work. That means we will have to take
- * care of kvm_put_kvm.
- */
- kvm_put_kvm(kvm);
+ /*
+ * In kvm_free_device_irq, cancel_work_sync return true if:
+ * 1. work is scheduled, and then cancelled.
+ * 2. work callback is executed.
+ *
+ * The first one ensured that the irq is disabled and no more events
+ * would happen. But for the second one, the irq may be enabled (e.g.
+ * for MSI). So we disable irq here to prevent further events.
+ *
+ * Notice this maybe result in nested disable if the interrupt type is
+ * INTx, but it's OK for we are going to free it.
+ *
+ * If this function is a part of VM destroy, please ensure that till
+ * now, the kvm state is still legal for probably we also have to wait
+ * interrupt_work done.
+ */
+ disable_irq_nosync(assigned_dev->host_irq);
+ cancel_work_sync(&assigned_dev->interrupt_work);
free_irq(assigned_dev->host_irq, (void *)assigned_dev);