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

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Message-ID: <e809be5b-0b24-34dc-1eae-82b58dc54545@de.ibm.com>
Date:   Mon, 21 Jun 2021 18:04:54 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>, jgg@...dia.com
Cc:     cohuck@...hat.com, pasic@...ux.vnet.ibm.com, jjherne@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        frankja@...ux.ibm.com, david@...hat.com, imbrenda@...ux.ibm.com,
        hca@...ux.ibm.com, Vasily Gorbik <gor@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/2] s390/vfio-ap: clean up mdev resources when remove
 callback invoked



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@...ux.ibm.com>
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Cc: stable@...r.kernel.org

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);
>