From: Tony Krowiak <akrowiak@linux.ibm.com>
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
Subject: Re: [PATCH v11 01/14] s390/vfio-ap: No need to disable IRQ after queue reset
Date: Fri, 30 Oct 2020 17:13:38 -0400 [thread overview]
Message-ID: <684234fa-03a9-71cd-14f3-ddf9b06e7e2e@linux.ibm.com> (raw)
In-Reply-To: <d1aae333-3f10-bd21-257f-baf8f8df7a24@linux.ibm.com>
On 10/30/20 4:53 PM, Tony Krowiak wrote:
>
>
> 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.
After thinking about this a bit more, I don't think it makes sense to make
this change in this patch. For the current implementation, it is incumbent
upon the system administrator to ensure that a queue device is not unbound
from the vfio_ap device driver if its APQN is assigned to an mdev, so the
assumption here is that any APQN assigned to the mdev is (or was) bound to
the vfio_ap driver. If it was erroneously unbound while in use by a guest,
then both the guest and possibly the zcrypt driver will have simultaneous
access (one of the things fixed by this patch series). In that case, I think
it ought to be reset regardless of whether it is bound to vfio_ap or not.
Having said that, I think it makes sense to make the change you recommend
in patch 03/14. In that patch, the vfio_ap_queue object is retrieved
from the
matrix_mdev. Since these queue objects are linked only when the queue
device is probed and unlinked when the the queue device is removed and
a queue device can not get bound to another driver while its APQN is
assigned
to an mdev, it would make perfect sense to forego reset of a queue when
its APQN is assigned to an mdev.
>
>
>
>
>>
>
next prev parent reply other threads:[~2020-10-30 21:13 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-22 17:11 [PATCH v11 00/14] s390/vfio-ap: dynamic configuration support Tony Krowiak
2020-10-22 17:11 ` [PATCH v11 01/14] s390/vfio-ap: No need to disable IRQ after queue reset Tony Krowiak
2020-10-22 19:44 ` kernel test robot
2020-10-26 16:57 ` Tony Krowiak
2020-10-27 6:48 ` Halil Pasic
2020-10-29 23:29 ` Tony Krowiak
2020-10-30 16:13 ` Tony Krowiak
2020-10-30 17:27 ` Halil Pasic
2020-10-30 20:45 ` Tony Krowiak
2020-10-30 17:42 ` Halil Pasic
2020-10-30 20:37 ` Tony Krowiak
2020-10-31 3:43 ` Halil Pasic
2020-11-02 14:35 ` Tony Krowiak
2020-10-30 17:54 ` Halil Pasic
2020-10-30 20:53 ` Tony Krowiak
2020-10-30 21:13 ` Tony Krowiak [this message]
2020-10-30 17:56 ` Halil Pasic
2020-10-30 21:17 ` Tony Krowiak
2020-10-22 17:11 ` [PATCH v11 02/14] 390/vfio-ap: use new AP bus interface to search for queue devices Tony Krowiak
2020-10-27 7:01 ` Halil Pasic
2020-11-02 21:57 ` Tony Krowiak
2020-10-22 17:11 ` [PATCH v11 03/14] s390/vfio-ap: manage link between queue struct and matrix mdev Tony Krowiak
2020-10-27 9:33 ` Halil Pasic
2020-10-22 17:11 ` [PATCH v11 04/14] s390/zcrypt: driver callback to indicate resource in use Tony Krowiak
2020-10-27 13:01 ` Halil Pasic
2020-10-27 16:55 ` Harald Freudenberger
2020-11-13 21:30 ` Tony Krowiak
2020-11-14 0:00 ` Halil Pasic
2020-11-16 16:23 ` Tony Krowiak
2020-10-22 17:12 ` [PATCH v11 05/14] s390/vfio-ap: implement in-use callback for vfio_ap driver Tony Krowiak
2020-10-27 13:27 ` Halil Pasic
2020-11-13 17:14 ` Tony Krowiak
2020-11-13 23:47 ` Halil Pasic
2020-11-16 16:58 ` Tony Krowiak
2020-11-23 17:03 ` Cornelia Huck
2020-11-23 19:23 ` Tony Krowiak
2020-10-22 17:12 ` [PATCH v11 06/14] s390/vfio-ap: introduce shadow APCB Tony Krowiak
2020-10-28 8:11 ` Halil Pasic
2020-11-13 17:18 ` Tony Krowiak
2020-10-22 17:12 ` [PATCH v11 07/14] s390/vfio-ap: sysfs attribute to display the guest's matrix Tony Krowiak
2020-10-28 8:17 ` Halil Pasic
2020-11-13 17:27 ` Tony Krowiak
2020-11-13 23:12 ` Halil Pasic
2020-11-19 18:15 ` Tony Krowiak
2020-10-22 17:12 ` [PATCH v11 08/14] s390/vfio-ap: hot plug/unplug queues on bind/unbind of queue device Tony Krowiak
2020-10-22 20:30 ` kernel test robot
2020-10-26 17:04 ` Tony Krowiak
2020-10-28 13:57 ` Halil Pasic
2020-11-03 22:49 ` Tony Krowiak
2020-11-04 12:52 ` Halil Pasic
2020-11-04 21:20 ` Tony Krowiak
2020-11-05 12:27 ` Halil Pasic
2020-11-13 20:36 ` Tony Krowiak
2020-11-04 13:23 ` Halil Pasic
2020-10-22 17:12 ` [PATCH v11 09/14] s390/vfio-ap: allow assignment of unavailable AP queues to mdev device Tony Krowiak
2020-10-28 15:03 ` Halil Pasic
2020-10-22 17:12 ` [PATCH v11 10/14] s390/vfio-ap: allow hot plug/unplug of AP resources using " Tony Krowiak
2020-10-22 17:12 ` [PATCH v11 11/14] s390/zcrypt: Notify driver on config changed and scan complete callbacks Tony Krowiak
2020-10-27 17:28 ` Harald Freudenberger
2020-11-13 20:58 ` Tony Krowiak
2020-10-22 17:12 ` [PATCH v11 12/14] s390/vfio-ap: handle host AP config change notification Tony Krowiak
2020-10-22 21:17 ` kernel test robot
2020-10-26 17:07 ` Tony Krowiak
2020-10-26 17:21 ` Tony Krowiak
2020-11-03 9:48 ` kernel test robot
2020-11-13 21:06 ` Tony Krowiak
2020-10-22 17:12 ` [PATCH v11 13/14] s390/vfio-ap: handle AP bus scan completed notification Tony Krowiak
2020-10-22 17:12 ` [PATCH v11 14/14] s390/vfio-ap: update docs to include dynamic config support Tony Krowiak
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