[PATCH v2 13/15] vfio/ccw: Use the new device life cycle helpers

Kevin Tian
2022-09-01T07:21:38Z

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@nvidia.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
---
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 c9d982131265..957d9f286550 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -481,28 +481,13 @@ 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
@@ -560,7 +545,9 @@ 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);
@@ -572,7 +559,7 @@ 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 e1e9e8352903..f03447c8774d 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -160,9 +160,6 @@ 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