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Subject: Re: [PATCH v11 01/14] s390/vfio-ap: No need to disable IRQ after
 queue reset
To:     Halil Pasic <pasic@linux.ibm.com>
Cc:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, freude@linux.ibm.com, borntraeger@de.ibm.com,
        cohuck@redhat.com, mjrosato@linux.ibm.com,
        alex.williamson@redhat.com, kwankhede@nvidia.com,
        fiuczy@linux.ibm.com, frankja@linux.ibm.com, david@redhat.com,
        hca@linux.ibm.com, gor@linux.ibm.com
References: <20201022171209.19494-1-akrowiak@linux.ibm.com>
 <20201022171209.19494-2-akrowiak@linux.ibm.com>
 <20201027074846.30ee0ddc.pasic@linux.ibm.com>
 <7a2c5930-9c37-8763-7e5d-c08a3638e6a1@linux.ibm.com>
 <20201030185406.7fa13fbe.pasic@linux.ibm.com>
From:   Tony Krowiak <akrowiak@linux.ibm.com>
Message-ID: <d1aae333-3f10-bd21-257f-baf8f8df7a24@linux.ibm.com>
Date:   Fri, 30 Oct 2020 16:53:04 -0400
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On 10/30/20 1:54 PM, Halil Pasic wrote:
> On Thu, 29 Oct 2020 19:29:35 -0400
> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
>
>>>> @@ -1177,7 +1166,10 @@ static int vfio_ap_mdev_reset_queues(struct mdev_device *mdev)
>>>>    			 */
>>>>    			if (ret)
>>>>    				rc = ret;
>>>> -			vfio_ap_irq_disable_apqn(AP_MKQID(apid, apqi));
>>>> +			q = vfio_ap_get_queue(matrix_mdev,
>>>> +					      AP_MKQID(apid, apqi));
>>>> +			if (q)
>>>> +				vfio_ap_free_aqic_resources(q);
> [..]
>
>>> Under what circumstances do we expect !q? If we don't, then we need to
>>> complain one way or another.
>> In the current code (i.e., prior to introducing the subsequent hot
>> plug patches), an APQN can not be assigned to an mdev unless it
>> references a queue device bound to the vfio_ap device driver; however,
>> there is nothing preventing a queue device from getting unbound
>> while the guest is running (one of the problems mostly resolved by this
>> series). In that case, q would be NULL.
> But if the queue does not belong to us any more it does not make sense
> call vfio_ap_mdev_reset_queue() on it's APQN, or?

This is precisely why we prevent a queue from being taken away
from vfio_ap (the in-use callback) when its APQN is assigned to an
mdev in this patch series. On the other hand, this is a very good
point.

>
> I think we should have
>
> if(!q)
> 	continue;
> at the very beginning of the loop body, or we want to be sure that q is
> not null.

I agree, I'll go ahead and make this change.


>   
>