vfio: Try to enable IOPF for VFIO devices

If IOMMU_DEV_FEAT_IOPF is set for the VFIO device, which means that
the delivering of page faults of this device from the IOMMU is enabled,
we register the VFIO page fault handler to complete the whole faulting
path (HW+SW). And add a iopf_enabled field in struct vfio_device to
record it.

Signed-off-by: Shenming Lu <lushenming@huawei.com>

drivers/vfio/vfio.c

@@ -97,6 +97,7 @@ struct vfio_device {
 	struct vfio_group		*group;
 	struct list_head		group_next;
 	void				*device_data;
+	bool				iopf_enabled;
 };
 
 #ifdef CONFIG_VFIO_NOIOMMU
@@ -532,6 +533,21 @@ static struct vfio_group *vfio_group_get_from_dev(struct device *dev)
 /**
  * Device objects - create, release, get, put, search
  */
+
+static void vfio_device_enable_iopf(struct vfio_device *device)
+{
+	struct device *dev = device->dev;
+
+	if (!iommu_dev_has_feature(dev, IOMMU_DEV_FEAT_IOPF))
+		return;
+
+	if (WARN_ON(iommu_register_device_fault_handler(dev,
+					vfio_iommu_dev_fault_handler, dev)))
+		return;
+
+	device->iopf_enabled = true;
+}
+
 static
 struct vfio_device *vfio_group_create_device(struct vfio_group *group,
 					     struct device *dev,
@@ -549,6 +565,8 @@ struct vfio_device *vfio_group_create_device(struct vfio_group *group,
 	device->group = group;
 	device->ops = ops;
 	device->device_data = device_data;
+	/* By default try to enable IOPF */
+	vfio_device_enable_iopf(device);
 	dev_set_drvdata(dev, device);
 
 	/* No need to get group_lock, caller has group reference */
@@ -573,6 +591,8 @@ static void vfio_device_release(struct kref *kref)
 	mutex_unlock(&group->device_lock);
 
 	dev_set_drvdata(device->dev, NULL);
+	if (device->iopf_enabled)
+		WARN_ON(iommu_unregister_device_fault_handler(device->dev));
 
 	kfree(device);