[PATCH v3 13/15] vfio/ccw: Use the new device life cycle helpers

[Kevin Tian]

ccw is the only exception which cannot use vfio_alloc_device() because
its private device structure is designed to serve both mdev and parent.
Life cycle of the parent is managed by css_driver so vfio_ccw_private
must be allocated/freed in css_driver probe/remove path instead of
conforming to vfio core life cycle for mdev.

Given that use a wait/completion scheme so the mdev remove path waits
after vfio_put_device() until receiving a completion notification from
@release. The completion indicates that all active references on
vfio_device have been released.

After that point although free of vfio_ccw_private is delayed to
css_driver it's at least guaranteed to have no parallel reference on
released vfio device part from other code paths.

memset() in @probe is removed. vfio_device is either already cleared
when probed for the first time or cleared in @release from last probe.

The right fix is to introduce separate structures for mdev and parent,
but this won't happen in short term per prior discussions.

Remove vfio_init/uninit_group_dev() as no user now.

Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Kevin Tian <kevin.tian@xxxxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Reviewed-by: Eric Farman <farman@xxxxxxxxxxxxx>
---
 drivers/s390/cio/vfio_ccw_ops.c     | 52 +++++++++++++++++++++++++----
 drivers/s390/cio/vfio_ccw_private.h |  3 ++
 drivers/vfio/vfio_main.c            | 23 +++----------
 include/linux/vfio.h                |  3 --
 4 files changed, 53 insertions(+), 28 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
index 4a806a2273b5..9f8486c0d3d3 100644
--- a/drivers/s390/cio/vfio_ccw_ops.c
+++ b/drivers/s390/cio/vfio_ccw_ops.c
@@ -87,6 +87,15 @@ static struct attribute_group *mdev_type_groups[] = {
 	NULL,
 };
 
+static int vfio_ccw_mdev_init_dev(struct vfio_device *vdev)
+{
+	struct vfio_ccw_private *private =
+		container_of(vdev, struct vfio_ccw_private, vdev);
+
+	init_completion(&private->release_comp);
+	return 0;
+}
+
 static int vfio_ccw_mdev_probe(struct mdev_device *mdev)
 {
 	struct vfio_ccw_private *private = dev_get_drvdata(mdev->dev.parent);
@@ -98,9 +107,9 @@ static int vfio_ccw_mdev_probe(struct mdev_device *mdev)
 	if (atomic_dec_if_positive(&private->avail) < 0)
 		return -EPERM;
 
-	memset(&private->vdev, 0, sizeof(private->vdev));
-	vfio_init_group_dev(&private->vdev, &mdev->dev,
-			    &vfio_ccw_dev_ops);
+	ret = vfio_init_device(&private->vdev, &mdev->dev, &vfio_ccw_dev_ops);
+	if (ret)
+		return ret;
 
 	VFIO_CCW_MSG_EVENT(2, "sch %x.%x.%04x: create\n",
 			   private->sch->schid.cssid,
@@ -109,16 +118,33 @@ static int vfio_ccw_mdev_probe(struct mdev_device *mdev)
 
 	ret = vfio_register_emulated_iommu_dev(&private->vdev);
 	if (ret)
-		goto err_atomic;
+		goto err_put_vdev;
 	dev_set_drvdata(&mdev->dev, private);
 	return 0;
 
-err_atomic:
-	vfio_uninit_group_dev(&private->vdev);
+err_put_vdev:
+	vfio_put_device(&private->vdev);
 	atomic_inc(&private->avail);
 	return ret;
 }
 
+static void vfio_ccw_mdev_release_dev(struct vfio_device *vdev)
+{
+	struct vfio_ccw_private *private =
+		container_of(vdev, struct vfio_ccw_private, vdev);
+
+	/*
+	 * We cannot free vfio_ccw_private here because it includes
+	 * parent info which must be free'ed by css driver.
+	 *
+	 * Use a workaround by memset'ing the core device part and
+	 * then notifying the remove path that all active references
+	 * to this device have been released.
+	 */
+	memset(vdev, 0, sizeof(*vdev));
+	complete(&private->release_comp);
+}
+
 static void vfio_ccw_mdev_remove(struct mdev_device *mdev)
 {
 	struct vfio_ccw_private *private = dev_get_drvdata(mdev->dev.parent);
@@ -130,7 +156,17 @@ static void vfio_ccw_mdev_remove(struct mdev_device *mdev)
 
 	vfio_unregister_group_dev(&private->vdev);
 
-	vfio_uninit_group_dev(&private->vdev);
+	vfio_put_device(&private->vdev);
+	/*
+	 * Wait for all active references on mdev are released so it
+	 * is safe to defer kfree() to a later point.
+	 *
+	 * TODO: the clean fix is to split parent/mdev info from ccw
+	 * private structure so each can be managed in its own life
+	 * cycle.
+	 */
+	wait_for_completion(&private->release_comp);
+
 	atomic_inc(&private->avail);
 }
 
@@ -592,6 +628,8 @@ static void vfio_ccw_mdev_request(struct vfio_device *vdev, unsigned int count)
 }
 
 static const struct vfio_device_ops vfio_ccw_dev_ops = {
+	.init = vfio_ccw_mdev_init_dev,
+	.release = vfio_ccw_mdev_release_dev,
 	.open_device = vfio_ccw_mdev_open_device,
 	.close_device = vfio_ccw_mdev_close_device,
 	.read = vfio_ccw_mdev_read,
diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h
index cd24b7fada91..63d9202b29c7 100644
--- a/drivers/s390/cio/vfio_ccw_private.h
+++ b/drivers/s390/cio/vfio_ccw_private.h
@@ -88,6 +88,7 @@ struct vfio_ccw_crw {
  * @req_trigger: eventfd ctx for signaling userspace to return device
  * @io_work: work for deferral process of I/O handling
  * @crw_work: work for deferral process of CRW handling
+ * @release_comp: synchronization helper for vfio device release
  */
 struct vfio_ccw_private {
 	struct vfio_device vdev;
@@ -113,6 +114,8 @@ struct vfio_ccw_private {
 	struct eventfd_ctx	*req_trigger;
 	struct work_struct	io_work;
 	struct work_struct	crw_work;
+
+	struct completion	release_comp;
 } __aligned(8);
 
 int vfio_ccw_sch_quiesce(struct subchannel *sch);
diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index adc1b697bb78..5bc221730d7b 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -483,28 +483,13 @@ static struct vfio_device *vfio_group_get_device(struct vfio_group *group,
 /*
  * VFIO driver API
  */
-void vfio_init_group_dev(struct vfio_device *device, struct device *dev,
-			 const struct vfio_device_ops *ops)
-{
-	init_completion(&device->comp);
-	device->dev = dev;
-	device->ops = ops;
-}
-EXPORT_SYMBOL_GPL(vfio_init_group_dev);
-
-void vfio_uninit_group_dev(struct vfio_device *device)
-{
-	vfio_release_device_set(device);
-}
-EXPORT_SYMBOL_GPL(vfio_uninit_group_dev);
-
 /* Release helper called by vfio_put_device() */
 void vfio_device_release(struct kref *kref)
 {
 	struct vfio_device *device =
 			container_of(kref, struct vfio_device, kref);
 
-	vfio_uninit_group_dev(device);
+	vfio_release_device_set(device);
 
 	/*
 	 * kvfree() cannot be done here due to a life cycle mess in
@@ -562,7 +547,9 @@ int vfio_init_device(struct vfio_device *device, struct device *dev,
 {
 	int ret;
 
-	vfio_init_group_dev(device, dev, ops);
+	init_completion(&device->comp);
+	device->dev = dev;
+	device->ops = ops;
 
 	if (ops->init) {
 		ret = ops->init(device);
@@ -574,7 +561,7 @@ int vfio_init_device(struct vfio_device *device, struct device *dev,
 	return 0;
 
 out_uninit:
-	vfio_uninit_group_dev(device);
+	vfio_release_device_set(device);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(vfio_init_device);
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index f67cac700e6f..3cf857b1eec7 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -184,9 +184,6 @@ static inline void vfio_put_device(struct vfio_device *device)
 	kref_put(&device->kref, vfio_device_release);
 }
 
-void vfio_init_group_dev(struct vfio_device *device, struct device *dev,
-			 const struct vfio_device_ops *ops);
-void vfio_uninit_group_dev(struct vfio_device *device);
 int vfio_register_group_dev(struct vfio_device *device);
 int vfio_register_emulated_iommu_dev(struct vfio_device *device);
 void vfio_unregister_group_dev(struct vfio_device *device);
-- 
2.21.3