linux-kernel - Re: [PATCH v16 06/14] s390/vfio-ap: refresh guest's APCB by filtering APQNs assigned to mdev

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Message-ID: <20210524181548.4dbe52bc.pasic@linux.ibm.com>
Date:   Mon, 24 May 2021 18:15:48 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, jjherne@...ux.ibm.com, freude@...ux.ibm.com,
        borntraeger@...ibm.com, cohuck@...hat.com, mjrosato@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        fiuczy@...ux.ibm.com
Subject: Re: [PATCH v16 06/14] s390/vfio-ap: refresh guest's APCB by
 filtering APQNs assigned to mdev

On Mon, 10 May 2021 12:44:15 -0400
Tony Krowiak <akrowiak@...ux.ibm.com> wrote:

> @@ -1601,8 +1676,10 @@ void vfio_ap_mdev_remove_queue(struct ap_device *apdev)
>  	mutex_lock(&matrix_dev->lock);
>  	q = dev_get_drvdata(&apdev->device);
>  
> -	if (q->matrix_mdev)
> +	if (q->matrix_mdev) {
>  		vfio_ap_mdev_unlink_queue_fr_mdev(q);
> +		vfio_ap_mdev_refresh_apcb(q->matrix_mdev);
> +	}
>  
>  	vfio_ap_mdev_reset_queue(q, 1);
>  	dev_set_drvdata(&apdev->device, NULL);

At this point we don't know if !!kvm_busy or kvm_busy AFAICT. If
!!kvm_busy, then we may end up changing a shadow_apcb while an other
thread is in the middle of committing it to the SD satellite. That
would be no good.

Regards,
Halil