linux-kernel - Re: [PATCH 1/3] s390/vfio-ap: clean up mdev resources when remove callback invoked

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Date:   Fri, 11 Jun 2021 13:48:54 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        borntraeger@...ibm.com, 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
Subject: Re: [PATCH 1/3] s390/vfio-ap: clean up mdev resources when remove
 callback invoked

On Wed, Jun 09, 2021 at 06:46:32PM -0400, 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>
> ---
>  drivers/s390/crypto/vfio_ap_ops.c | 10 ----------
>  1 file changed, 10 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason