KVM: destruct kvm_io_device while unregistering it from kvm_io_bus

Current usage of kvm_io_device requires users to destruct it with an extra
call of kvm_iodevice_destructor after the device gets unregistered from
kvm_io_bus. This is not necessary and can cause errors if a user forgot
to make the extra call.

Simplify the usage by combining kvm_iodevice_destructor into
kvm_io_bus_unregister_dev. This reduces LOCs a bit for users and can
avoid the leakage of destructing the device explicitly.

Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20230207123713.3905-2-wei.w.wang@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: wei-w-wang

include/kvm/iodev.h

@@ -55,10 +55,4 @@ static inline int kvm_iodevice_write(struct kvm_vcpu *vcpu,
 				 : -EOPNOTSUPP;
 }
 
-static inline void kvm_iodevice_destructor(struct kvm_io_device *dev)
-{
-	if (dev->ops->destructor)
-		dev->ops->destructor(dev);
-}
-
 #endif /* __KVM_IODEV_H__ */

virt/kvm/coalesced_mmio.c

@@ -186,15 +186,10 @@ int kvm_vm_ioctl_unregister_coalesced_mmio(struct kvm *kvm,
 		    coalesced_mmio_in_range(dev, zone->addr, zone->size)) {
 			r = kvm_io_bus_unregister_dev(kvm,
 				zone->pio ? KVM_PIO_BUS : KVM_MMIO_BUS, &dev->dev);
-
-			kvm_iodevice_destructor(&dev->dev);
-
 			/*
 			 * On failure, unregister destroys all devices on the
-			 * bus _except_ the target device, i.e. coalesced_zones
-			 * has been modified.  Bail after destroying the target
-			 * device, there's no need to restart the walk as there
-			 * aren't any zones left.
+			 * bus, including the target device. There's no need
+			 * to restart the walk as there aren't any zones left.
 			 */
 			if (r)
 				break;

virt/kvm/eventfd.c

@@ -931,7 +931,6 @@ kvm_deassign_ioeventfd_idx(struct kvm *kvm, enum kvm_bus bus_idx,
 		bus = kvm_get_bus(kvm, bus_idx);
 		if (bus)
 			bus->ioeventfd_count--;
-		ioeventfd_release(p);
 		ret = 0;
 		break;
 	}

virt/kvm/kvm_main.c

@@ -5297,6 +5297,12 @@ static void hardware_disable_all(void)
 }
 #endif /* CONFIG_KVM_GENERIC_HARDWARE_ENABLING */
 
+static void kvm_iodevice_destructor(struct kvm_io_device *dev)
+{
+	if (dev->ops->destructor)
+		dev->ops->destructor(dev);
+}
+
 static void kvm_io_bus_destroy(struct kvm_io_bus *bus)
 {
 	int i;
@@ -5520,7 +5526,7 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
 			      struct kvm_io_device *dev)
 {
-	int i, j;
+	int i;
 	struct kvm_io_bus *new_bus, *bus;
 
 	lockdep_assert_held(&kvm->slots_lock);
@@ -5550,18 +5556,19 @@ int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
 	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
 	synchronize_srcu_expedited(&kvm->srcu);
 
-	/* Destroy the old bus _after_ installing the (null) bus. */
+	/*
+	 * If NULL bus is installed, destroy the old bus, including all the
+	 * attached devices. Otherwise, destroy the caller's device only.
+	 */
 	if (!new_bus) {
 		pr_err("kvm: failed to shrink bus, removing it completely\n");
-		for (j = 0; j < bus->dev_count; j++) {
-			if (j == i)
-				continue;
-			kvm_iodevice_destructor(bus->range[j].dev);
-		}
+		kvm_io_bus_destroy(bus);
+		return -ENOMEM;
 	}
 
+	kvm_iodevice_destructor(dev);
 	kfree(bus);
-	return new_bus ? 0 : -ENOMEM;
+	return 0;
 }
 
 struct kvm_io_device *kvm_io_bus_get_dev(struct kvm *kvm, enum kvm_bus bus_idx,