Re: [PATCH 14/14] vfio/mdev: add mdev available instance checking to the core

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

On Mon, 2022-08-22 at 08:22 +0200, Christoph Hellwig wrote:
> Many of the mdev drivers use a simple counter for keeping track of
> the
> available instances. Move this code to the core code and store the
> counter
> in the mdev_parent. Implement it using correct locking, fixing mdpy.
> 
> Drivers just provide the value in the mdev_driver at registration
> time
> and the core code takes care of maintaining it and exposing the value
> in
> sysfs.
> 
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> [hch: count instances per-parent instead of per-type, use an atomic_t
>  to avoid taking mdev_list_lock in the show method]
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Kirti Wankhede <kwankhede@nvidia.com>

...snip...

> diff --git a/drivers/vfio/mdev/mdev_core.c
> b/drivers/vfio/mdev/mdev_core.c
> index 93f8caf2e5f77..2d0302995d7b7 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -70,6 +70,7 @@ int mdev_register_parent(struct mdev_parent
> *parent, struct device *dev,
>         parent->mdev_driver = mdev_driver;
>         parent->types = types;
>         parent->nr_types = nr_types;
> +       atomic_set(&parent->available_instances, mdev_driver-
> >max_instances);
>  
>         if (!mdev_bus_compat_class) {
>                 mdev_bus_compat_class =
> class_compat_register("mdev_bus");
> @@ -115,14 +116,17 @@ EXPORT_SYMBOL(mdev_unregister_parent);
>  static void mdev_device_release(struct device *dev)
>  {
>         struct mdev_device *mdev = to_mdev_device(dev);
> -
> -       /* Pairs with the get in mdev_device_create() */
> -       kobject_put(&mdev->type->kobj);
> +       struct mdev_parent *parent = mdev->type->parent;
>  
>         mutex_lock(&mdev_list_lock);
>         list_del(&mdev->next);
> +       if (!parent->mdev_driver->get_available)
> +               atomic_inc(&parent->available_instances);
>         mutex_unlock(&mdev_list_lock);
>  
> +       /* Pairs with the get in mdev_device_create() */
> +       kobject_put(&mdev->type->kobj);
> +
>         dev_dbg(&mdev->dev, "MDEV: destroying\n");
>         kfree(mdev);
>  }
> @@ -144,6 +148,13 @@ int mdev_device_create(struct mdev_type *type,
> const guid_t *uuid)
>                 }
>         }
>  
> +       if (!drv->get_available) {
> +               if (atomic_dec_and_test(&parent-
> >available_instances)) {

This is still broken.

https://lore.kernel.org/r/20220719144808.GA21431@lst.de/

Thanks,
Eric

> +                       mutex_unlock(&mdev_list_lock);
> +                       return -EUSERS;
> +               }
> +       }
> +