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

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Date:   Mon, 6 May 2019 15:37:37 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     pmorel@...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 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?

> 
>>               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.

> 
> 
> 
>>               /*
>>                * 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.

> 
>>
> 
>