Re: [PATCH v5 07/10] vfio: Add helper to search vfio_device in a dev_set

[Alex Williamson <alex.williamson@redhat.com>]

On Sat, 13 May 2023 06:21:33 -0700
Yi Liu <yi.l.liu@intel.com> wrote:

> There are drivers that need to search vfio_device within a given dev_set.
> e.g. vfio-pci. So add a helper.
> 
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c |  8 +++-----
>  drivers/vfio/vfio_main.c         | 15 +++++++++++++++
>  include/linux/vfio.h             |  3 +++
>  3 files changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 39e7823088e7..4df2def35bdd 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -2335,12 +2335,10 @@ static bool vfio_dev_in_groups(struct vfio_pci_core_device *vdev,
>  static int vfio_pci_is_device_in_set(struct pci_dev *pdev, void *data)
>  {
>  	struct vfio_device_set *dev_set = data;
> -	struct vfio_device *cur;
>  
> -	list_for_each_entry(cur, &dev_set->device_list, dev_set_list)
> -		if (cur->dev == &pdev->dev)
> -			return 0;
> -	return -EBUSY;
> +	lockdep_assert_held(&dev_set->lock);
> +
> +	return vfio_find_device_in_devset(dev_set, &pdev->dev) ? 0 : -EBUSY;

Maybe an opportunity to revisit why this returns -EBUSY rather than
something reasonable like -ENODEV.  It looks like we picked up the
-EBUSY in a882c16a2b7e where I think it was trying to preserve the
return of vfio_pci_try_zap_and_vma_lock_cb() but the return value here
is not even propagated so this looks like an chance to have it make
sense again.  Thanks,

Alex

>  }
>  
>  /*
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index f0ca33b2e1df..ab4f3a794f78 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -141,6 +141,21 @@ unsigned int vfio_device_set_open_count(struct vfio_device_set *dev_set)
>  }
>  EXPORT_SYMBOL_GPL(vfio_device_set_open_count);
>  
> +struct vfio_device *
> +vfio_find_device_in_devset(struct vfio_device_set *dev_set,
> +			   struct device *dev)
> +{
> +	struct vfio_device *cur;
> +
> +	lockdep_assert_held(&dev_set->lock);
> +
> +	list_for_each_entry(cur, &dev_set->device_list, dev_set_list)
> +		if (cur->dev == dev)
> +			return cur;
> +	return NULL;
> +}
> +EXPORT_SYMBOL_GPL(vfio_find_device_in_devset);
> +
>  /*
>   * Device objects - create, release, get, put, search
>   */
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index fcbe084b18c8..4c17395ed4d2 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -259,6 +259,9 @@ void vfio_unregister_group_dev(struct vfio_device *device);
>  
>  int vfio_assign_device_set(struct vfio_device *device, void *set_id);
>  unsigned int vfio_device_set_open_count(struct vfio_device_set *dev_set);
> +struct vfio_device *
> +vfio_find_device_in_devset(struct vfio_device_set *dev_set,
> +			   struct device *dev);
>  
>  int vfio_mig_get_next_state(struct vfio_device *device,
>  			    enum vfio_device_mig_state cur_fsm,