Re: [PATCH v6 1/2] s390/vfio-ap: clean up mdev resources when remove callback invoked

[Christian Borntraeger]

On 21.06.21 17:57, Tony Krowiak wrote:
> The mdev remove callback for the vfio_ap device driver bails out with
> -EBUSY if the mdev is in use by a KVM guest (i.e., the KVM pointer in the
> struct ap_matrix_mdev is not NULL). The intended purpose was
> to prevent the mdev from being removed while in use. There are two
> problems with this scenario:
>
> 1. Returning a non-zero return code from the remove callback does not
>     prevent the removal of the mdev.
>
> 2. The KVM pointer in the struct ap_matrix_mdev will always be NULL because
>     the remove callback will not get invoked until the mdev fd is closed.
>     When the mdev fd is closed, the mdev release callback is invoked and
>     clears the KVM pointer from the struct ap_matrix_mdev.
>
> Let's go ahead and remove the check for KVM in the remove callback and
> allow the cleanup of mdev resources to proceed.
>
> Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

This one is already queued on

https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/log/?h=fixes

Jason. Do you want this in stable? Then we should write a mail after merging.
> ---
>   drivers/s390/crypto/vfio_ap_ops.c | 10 ----------
>   1 file changed, 10 deletions(-)
>
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index b2c7e10dfdcd..122c85c22469 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -366,16 +366,6 @@ static int vfio_ap_mdev_remove(struct mdev_device *mdev)
>   	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>   
>   	mutex_lock(&matrix_dev->lock);
> -
> -	/*
> -	 * If the KVM pointer is in flux or the guest is running, disallow
> -	 * un-assignment of control domain.
> -	 */
> -	if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
> -		mutex_unlock(&matrix_dev->lock);
> -		return -EBUSY;
> -	}
> -
>   	vfio_ap_mdev_reset_queues(mdev);
>   	list_del(&matrix_mdev->node);
>   	kfree(matrix_mdev);