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

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Date:   Tue, 1 Jun 2021 07:25:55 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Halil Pasic <pasic@...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 5/24/21 12:15 PM, Halil Pasic wrote:
> 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.

No, that would not be a good thing, we should check for
that.

>
> Regards,
> Halil