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 16:37:04 -0400 [thread overview]
Message-ID: <cb40a506-4a17-3562-728c-cbb57cd99817@linux.ibm.com> (raw)
In-Reply-To: <20201030184242.3bceee09.pasic@linux.ibm.com>
On 10/30/20 1:42 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);
>>> Is it safe to do vfio_ap_free_aqic_resources() at this point? I don't
>>> think so. I mean does the current code (and vfio_ap_mdev_reset_queue()
>>> in particular guarantee that the reset is actually done when we arrive
>>> here)? BTW, I think we have a similar problem with the current code as
>>> well.
>> If the return code from the vfio_ap_mdev_reset_queue() function
>> is zero, then yes, we are guaranteed the reset was done and the
>> queue is empty.
> I've read up on this and I disagree. We should discuss this offline.
Maybe you are confusing things here; my statement is specific to the return
code from the vfio_ap_mdev_reset_queue() function, not the response code
from the PQAP(ZAPQ) instruction. The vfio_ap_mdev_reset_queue()
function issues the PQAP(ZAPQ) instruction and if the status response code
is 0 indicating the reset was successfully initiated, it waits for the
queue to empty. When the queue is empty, it returns 0 to indicate
the queue is reset. If the queue does not become empty after a period of
time,
it will issue a warning (WARN_ON_ONCE) and return 0. In that case, I suppose
there is no guarantee the reset was done, so maybe a change needs to be
made there such as a non-zero return code.
>
>> The function returns a non-zero return code if
>> the reset fails or the queue the reset did not complete within a given
>> amount of time, so maybe we shouldn't free AQIC resources when
>> we get a non-zero return code from the reset function?
>>
> If the queue is gone, or broken, it won't produce interrupts or poke the
> notifier bit, and we should clean up the AQIC resources.
True, which is what the code provided by this patch does; however,
the AQIC resources should be cleaned up only if the KVM pointer is
not NULL for reasons discussed elsewhere.
>
>
>> There are three occasions when the vfio_ap_mdev_reset_queues()
>> is called:
>> 1. When the VFIO_DEVICE_RESET ioctl is invoked from userspace
>> (i.e., when the guest is started)
>> 2. When the mdev fd is closed (vfio_ap_mdev_release())
>> 3. When the mdev is removed (vfio_ap_mdev_remove())
>>
>> The IRQ resources are initialized when the PQAP(AQIC)
>> is intercepted to enable interrupts. This would occur after
>> the guest boots and the AP bus initializes. So, 1 would
>> presumably occur before that happens. I couldn't find
>> anywhere in the AP bus or zcrypt code where a PQAP(AQIC)
>> is executed to disable interrupts, so my assumption is
>> that IRQ disablement is accomplished by a reset on
>> the guest. I'll have to ask Harald about that. So, 2 would
>> occur when the guest is about to terminate and 3
>> would occur only after the guest is terminated. In any
>> case, it seems that IRQ resources should be cleaned up.
>> Maybe it would be more appropriate to do that in the
>> vfio_ap_mdev_release() and vfio_ap_mdev_remove()
>> functions themselves?
> I'm a bit confused. But I think you are wrong. What happens when the
> guest reIPLs? I guess the subsystem reset should also do the
> VFIO_DEVICE_RESET ioctl, and that has to reset the queues and disable
> the interrupts. Or?
What did I say that is wrong? I think you are referring
to my statement about the VFIO_DEVICE_RESET ioctl.
I am not knowledgeable about all of the circumstances
under which the VFIO_DEVICE_RESET ioctl is invoked,
but I know for a fact that it is invoked when the guest is
started as I've verified that via tracing. On the other hand,
I suspect you are correct in assuming it is also invoked on
a subsystem reset from the guest, so that also argues for
cleaning up the IRQ resources after a reset as long as
the KVM pointer is valid.
>
> Regards,
> Halil
>
next prev parent reply other threads:[~2020-10-30 20:37 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 [this message]
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
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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