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

[Eric Farman <farman@linux.ibm.com>]

On Thu, 2022-09-08 at 07:19 +0000, Tian, Kevin wrote:
> ping @Eric Farman.
> 
> ccw is the only tricky player in this series. Please help take a look
> in case of
> any oversight here.

Apologies, I had started looking at v1 before I left on holiday, and
only returned today.

> 
> > From: Tian, Kevin <kevin.tian@intel.com>
> > Sent: Thursday, September 1, 2022 10:38 PM
> > 
> > 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.

I did start looking at the above, while the mdev series is outstanding.
Will try to get back to that sooner rather than later, but for the
purposes of this series this patch looks/works fine to me.

Reviewed-by: Eric Farman <farman@linux.ibm.com>

> > 
> > 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
>