linux-kernel - Re: [PATCH v2 1/7] s390: vfio-ap: wait for queue empty on queue reset

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Date:   Tue, 7 May 2019 10:10:41 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     freude@...ux.ibm.com, borntraeger@...ibm.com, cohuck@...hat.com,
        frankja@...ux.ibm.com, david@...hat.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com
Subject: Re: [PATCH v2 1/7] s390: vfio-ap: wait for queue empty on queue reset

On 06/05/2019 21:37, Tony Krowiak wrote:
> On 5/6/19 2:41 AM, Pierre Morel wrote:
>> On 03/05/2019 23:14, Tony Krowiak wrote:
>>> Refactors the AP queue reset function to wait until the queue is empty
>>> after the PQAP(ZAPQ) instruction is executed to zero out the queue as
>>> required by the AP architecture.
>>>
>>> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
>>> ---
>>>   drivers/s390/crypto/vfio_ap_ops.c | 35 
>>> ++++++++++++++++++++++++++++++++---
>>>   1 file changed, 32 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c 
>>> b/drivers/s390/crypto/vfio_ap_ops.c
>>> index 900b9cf20ca5..b88a2a2ba075 100644
>>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>>> @@ -271,6 +271,32 @@ static int vfio_ap_mdev_verify_no_sharing(struct 
>>> ap_matrix_mdev *matrix_mdev)
>>>       return 0;
>>>   }
>>> +static void vfio_ap_mdev_wait_for_qempty(unsigned long apid, 
>>> unsigned long apqi)
>>> +{
>>> +    struct ap_queue_status status;
>>> +    ap_qid_t qid = AP_MKQID(apid, apqi);
>>> +    int retry = 5;
>>> +
>>> +    do {
>>> +        status = ap_tapq(qid, NULL);
>>> +        switch (status.response_code) {
>>> +        case AP_RESPONSE_NORMAL:
>>> +            if (status.queue_empty)
>>> +                return;
>>> +            msleep(20);
>>
>> NIT:     Fall through ?
> 
> Yes
> 
>>
>>> +            break;
>>> +        case AP_RESPONSE_RESET_IN_PROGRESS:
>>> +        case AP_RESPONSE_BUSY:
>>> +            msleep(20);
>>> +            break;
>>> +        default:
>>> +            pr_warn("%s: tapq err %02x: %04lx.%02lx may not be 
>>> empty\n",
>>> +                __func__, status.response_code, apid, apqi);
>>
>> I do not thing the warning sentence is appropriate:
>> The only possible errors here are if the AP is not available due to AP 
>> checkstop, deconfigured AP or invalid APQN.
> 
> Right you are! I'll work on a new message.
> 
>>
>>
>>> +            return;
>>> +        }
>>> +    } while (--retry);
>>> +}
>>> +
>>>   /**
>>>    * assign_adapter_store
>>>    *
>>> @@ -790,15 +816,18 @@ static int vfio_ap_mdev_group_notifier(struct 
>>> notifier_block *nb,
>>>       return NOTIFY_OK;
>>>   }
>>> -static int vfio_ap_mdev_reset_queue(unsigned int apid, unsigned int 
>>> apqi,
>>> -                    unsigned int retry)
>>> +int vfio_ap_mdev_reset_queue(unsigned int apid, unsigned int apqi)
>>>   {
>>>       struct ap_queue_status status;
>>> +    int retry = 5;
>>>       do {
>>>           status = ap_zapq(AP_MKQID(apid, apqi));
>>>           switch (status.response_code) {
>>>           case AP_RESPONSE_NORMAL:
>>> +            vfio_ap_mdev_wait_for_qempty(apid, apqi);
>>> +            return 0;
>>> +        case AP_RESPONSE_DECONFIGURED:
>>
>> Since you modify the switch, you can return for all the following cases:
>> AP_RESPONSE_DECONFIGURE
>> ..._CHECKSTOP
>> ..._INVALID_APQN
>>
>>
>> And you should wait for qempty on AP_RESET_IN_PROGRESS along with 
>> AP_RESPONSE_NORMAL
> 
> If a queue reset is in progress, we retry the zapq. Are you saying we
> should wait for qempty then reissue the zapq?


Yes, I fear that if we reissue the zapq while RESET is in progress we 
could fall in a loop depending on the reset hardware time and the 
software retry .

> 
>>
>>>               return 0;
>>>           case AP_RESPONSE_RESET_IN_PROGRESS:
>>>           case AP_RESPONSE_BUSY:
>>
>> While at modifying this function, the AP_RESPONSE_BUSY is not a valid 
>> code for ZAPQ, you can remove this.
> 
> Okay
> 
>>
>>> @@ -824,7 +853,7 @@ static int vfio_ap_mdev_reset_queues(struct 
>>> mdev_device *mdev)
>>>                    matrix_mdev->matrix.apm_max + 1) {
>>>           for_each_set_bit_inv(apqi, matrix_mdev->matrix.aqm,
>>>                        matrix_mdev->matrix.aqm_max + 1) {
>>> -            ret = vfio_ap_mdev_reset_queue(apid, apqi, 1);
>>> +            ret = vfio_ap_mdev_reset_queue(apid, apqi);
>>
>> IMHO, since you are at changing this call, passing the apqn as 
>> parameter would be a good simplification.
> 
> Okay.

Sorry, I should have add: NIT.

> 
>>
>>
>>
>>>               /*
>>>                * Regardless whether a queue turns out to be busy, or
>>>                * is not operational, we need to continue resetting
>>
>> Depends on why the reset failed, but this is out of scope.
> 
> I'm not sure what you mean by out of scope here, but you do make a valid
> point. If the response code for the zapq is AP_RESPONSE_DECONFIGURED,
> there is probably no sense in continuing to reset queues for that
> particular adapter. I'll consider a change here.

Yes, this was the point, but I consider this as a enhancement, trying a 
reset on bad queues AFAIK do no arm.

> 
>>
>>>
>>
>>
> 


-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany