Re: [PATCH v12 12/22] vfio: Add notifier callback to parent's ops structure of mdev

[Jike Song <jike.song@intel.com>]

On 11/14/2016 11:42 PM, Kirti Wankhede wrote:
> Add a notifier calback to parent's ops structure of mdev device so that per
> device notifer for vfio module is registered through vfio_mdev module.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> Signed-off-by: Neo Jia <cjia@nvidia.com>
> Change-Id: Iafa6f1721aecdd6e50eb93b153b5621e6d29b637
> ---
>  drivers/vfio/mdev/vfio_mdev.c | 19 +++++++++++++++++++
>  include/linux/mdev.h          |  9 +++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/vfio/mdev/vfio_mdev.c b/drivers/vfio/mdev/vfio_mdev.c
> index ffc36758cb84..1694b1635607 100644
> --- a/drivers/vfio/mdev/vfio_mdev.c
> +++ b/drivers/vfio/mdev/vfio_mdev.c
> @@ -24,6 +24,15 @@
>  #define DRIVER_AUTHOR   "NVIDIA Corporation"
>  #define DRIVER_DESC     "VFIO based driver for Mediated device"
>  
> +static int vfio_mdev_notifier(struct notifier_block *nb, unsigned long action,
> +			      void *data)
> +{
> +	struct mdev_device *mdev = container_of(nb, struct mdev_device, nb);
> +	struct parent_device *parent = mdev->parent;
> +
> +	return parent->ops->notifier(mdev, action, data);
> +}
> +
>  static int vfio_mdev_open(void *device_data)
>  {
>  	struct mdev_device *mdev = device_data;
> @@ -40,6 +49,11 @@ static int vfio_mdev_open(void *device_data)
>  	if (ret)
>  		module_put(THIS_MODULE);
>  
> +	if (likely(parent->ops->notifier)) {
> +		mdev->nb.notifier_call = vfio_mdev_notifier;
> +		if (vfio_register_notifier(&mdev->dev, &mdev->nb))
> +			pr_err("Failed to register notifier for mdev\n");
> +	}

Hi Kirti,

Could you please move the notifier registration before parent->ops->open()?
as you might know, I'm extending your vfio_register_notifier to also include
the attaching/detaching events of vfio_group and kvm.  Basically if vfio_group
not attached to any kvm instance, the parent->ops->open() should return -ENODEV
to indicate the failure, but to know whether kvm is available in open(), the
notifier registration should be earlier.

Of course I can call vfio_register_notifier() from an earlier place to
workaround it, but it doesn't seem a canonical way.

--
Thanks,
Jike

>  	return ret;
>  }
>  
> @@ -48,6 +62,11 @@ static void vfio_mdev_release(void *device_data)
>  	struct mdev_device *mdev = device_data;
>  	struct parent_device *parent = mdev->parent;
>  
> +	if (likely(parent->ops->notifier)) {
> +		if (vfio_unregister_notifier(&mdev->dev, &mdev->nb))
> +			pr_err("Failed to unregister notifier for mdev\n");
> +	}
> +
>  	if (likely(parent->ops->release))
>  		parent->ops->release(mdev);
>  
> diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> index 4900cc472364..665afe0a4c31 100644
> --- a/include/linux/mdev.h
> +++ b/include/linux/mdev.h
> @@ -37,6 +37,7 @@ struct mdev_device {
>  	struct kref		ref;
>  	struct list_head	next;
>  	struct kobject		*type_kobj;
> +	struct notifier_block	nb;
>  };
>  
>  /**
> @@ -85,6 +86,12 @@ struct mdev_device {
>   * @mmap:		mmap callback
>   *			@mdev: mediated device structure
>   *			@vma: vma structure
> + * @notifer:		Notifier callback, currently only for
> + *			VFIO_IOMMU_NOTIFY_DMA_UNMAP action notified duing
> + *			DMA_UNMAP call on mapped iova range.
> + *			@mdev: mediated device structure
> + *			@action: Action for which notifier is called
> + *			@data: Data associated with the notifier
>   * Parent device that support mediated device should be registered with mdev
>   * module with parent_ops structure.
>   **/
> @@ -106,6 +113,8 @@ struct parent_ops {
>  	ssize_t (*ioctl)(struct mdev_device *mdev, unsigned int cmd,
>  			 unsigned long arg);
>  	int	(*mmap)(struct mdev_device *mdev, struct vm_area_struct *vma);
> +	int	(*notifier)(struct mdev_device *mdev, unsigned long action,
> +			    void *data);
>  };
>  
>  /* interface for exporting mdev supported type attributes */
>