KVM: x86: race between KVM_SET_GSI_ROUTING and KVM_CREATE_IRQCHIP

Avoid races between KVM_SET_GSI_ROUTING and KVM_CREATE_IRQCHIP by taking
the kvm->lock when setting up routes.

If KVM_CREATE_IRQCHIP fails, KVM_SET_GSI_ROUTING could have already set
up routes pointing at pic/ioapic, being silently removed already.

Also, as a side effect, this patch makes sure that KVM_SET_GSI_ROUTING
and KVM_CAP_SPLIT_IRQCHIP cannot run in parallel.
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

virt/kvm/kvm_main.c

@@ -3069,8 +3069,11 @@ static long kvm_vm_ioctl(struct file *filp,
 					   routing.nr * sizeof(*entries)))
 				goto out_free_irq_routing;
 		}
+		/* avoid races with KVM_CREATE_IRQCHIP on x86 */
+		mutex_lock(&kvm->lock);
 		r = kvm_set_irq_routing(kvm, entries, routing.nr,
 					routing.flags);
+		mutex_unlock(&kvm->lock);
 out_free_irq_routing:
 		vfree(entries);
 		break;