Re: [RFC 02/20] vfio: Add device class for /dev/vfio/devices

Jason Gunthorpe
2021-11-03T13:25:55Z

On Tue, Nov 02, 2021 at 09:53:29AM +0000, Liu, Yi L wrote:

> > vfio_uninit_group_dev(&mdev_state->vdev);
> > kfree(mdev_state->pages);
> > kfree(mdev_state->vconfig);
> > kfree(mdev_state);
> >
> > pages/vconfig would logically be in a release function
>
> I see. So the criteria is: the pointer fields pointing to a memory buffer
> allocated by the device driver should be logically be free in a release
> function. right?

Often yes, that is usually a good idea

>I can see there are such fields in struct vfio_pci_core_device
> and mdev_state (both mbochs and mdpy). So we may go with your option #2.
> Is it? otherwise, needs to add release callback for all the related drivers.

Yes, that is the approx trade off

> > On the other hand ccw needs to rcu free the vfio_device, so that would
> > have to be global overhead with this api design.
>
> not quite get. why ccw is special here? could you elaborate?

I added a rcu usage to it in order to fix a race

+static inline struct vfio_ccw_private *vfio_ccw_get_priv(struct subchannel *sch)
+{
+ struct vfio_ccw_private *private;
+
+ rcu_read_lock();
+ private = dev_get_drvdata(&sch->dev);
+ if (private && !vfio_device_try_get(&private->vdev))
+ private = NULL;
+ rcu_read_unlock();
+ return private;
+}

Jason