linux-kernel - Re: [PATCH v6 2/7] s390: ap: new vfio_ap

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Message-Id: <0477b20a-c882-c23d-5373-d461ef721f2c@linux.ibm.com>
Date:   Thu, 28 Mar 2019 11:32:03 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     pmorel@...ux.ibm.com, borntraeger@...ibm.com
Cc:     alex.williamson@...hat.com, cohuck@...hat.com,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, frankja@...ux.ibm.com, pasic@...ux.ibm.com,
        david@...hat.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, freude@...ux.ibm.com, mimu@...ux.ibm.com
Subject: Re: [PATCH v6 2/7] s390: ap: new vfio_ap_queue structure

On 3/28/19 9:06 AM, Pierre Morel wrote:
> On 26/03/2019 21:45, Tony Krowiak wrote:
>> On 3/22/19 10:43 AM, Pierre Morel wrote:
>>> The AP interruptions are assigned on a queue basis and
>>> the GISA structure is handled on a VM basis, so that
>>> we need to add a structure we can retrieve from both side
>>
>> s/side/sides/
> OK
> 
>>
>>> holding the information we need to handle PQAP/AQIC interception
>>> and setup the GISA.
>>
>> s/setup/set up/
> 
> OK
> 
> ...snip...
> 
>>> +
>>> +static int vfio_ap_mdev_reset_queue(struct vfio_ap_queue *q)
>>> +{
>>> +    struct ap_queue_status status;
>>> +    int retry = 1;
>>> +
>>> +    do {
>>> +        status = ap_zapq(q->apqn);
>>> +        switch (status.response_code) {
>>> +        case AP_RESPONSE_NORMAL:
>>> +            return 0;
>>> +        case AP_RESPONSE_RESET_IN_PROGRESS:
>>> +        case AP_RESPONSE_BUSY:
>>> +            msleep(20);
>>> +            break;
>>> +        default:
>>> +            /* things are really broken, give up */
>>
>> I'm not sure things are necessarily broken. We could end up here if
>> the AP is removed from the configuration via the SE or SCLP Deconfigure
>> Adjunct Processor command.
> 
> OK, but note that it is your original comment I just moved the function 
> here ;)

Yes, it is. I'm smarter now;)

> 
>>
>>> +            return -EIO;
>>> +        }
>>> +    } while (retry--);
>>> +
>>> +    return -EBUSY;
>>> +}
>>> +
>>>   static void vfio_ap_matrix_init(struct ap_config_info *info,
>>>                   struct ap_matrix *matrix)
>>>   {
>>> @@ -45,6 +107,7 @@ static int vfio_ap_mdev_create(struct kobject 
>>> *kobj, struct mdev_device *mdev)
>>>           return -ENOMEM;
>>>       }
>>> +    INIT_LIST_HEAD(&matrix_mdev->qlist);
>>>       vfio_ap_matrix_init(&matrix_dev->info, &matrix_mdev->matrix);
>>>       mdev_set_drvdata(mdev, matrix_mdev);
>>>       mutex_lock(&matrix_dev->lock);
>>> @@ -113,162 +176,189 @@ static struct attribute_group 
>>> *vfio_ap_mdev_type_groups[] = {
>>>       NULL,
>>>   };
>>> -struct vfio_ap_queue_reserved {
>>> -    unsigned long *apid;
>>> -    unsigned long *apqi;
>>> -    bool reserved;
>>> -};
>>> +static void vfio_ap_free_queue(int apqn, struct ap_matrix_mdev 
>>> *matrix_mdev)
>>> +{
>>> +    struct vfio_ap_queue *q;
>>> +
>>> +    q = vfio_ap_get_queue(apqn, &matrix_mdev->qlist);
>>> +    if (!q)
>>> +        return;
>>> +    q->matrix_mdev = NULL;
>>> +    vfio_ap_mdev_reset_queue(q);
>>
>> I'm wondering if it's necessary to reset the queue here. The only time
>> a queue is used is when a guest using the mdev device is started. When
>> that guest is terminated, the fd for the mdev device is /* Bits 41-47 must all be zeros */closed and the
>> mdev device's release callback is invoked. The release callback resets
>> the queues assigned to the mdev device. Is it really necessary to
>> reset the queue again when it is unassigned even if there would have
>> been no subsequent activity?
> 
> Yes, it is necessary, the queue can be re-assigned to another guest later.
> Release will only be called when unbinding the queue from the driver.

That is true, but if the queue is never used, there is nothing to reset.

> 
>>
>>> +    list_move(&q->list, &matrix_dev->free_list);
>>> +}
> 
> ...snip...
> 
>>> +    for_each_set_bit_inv(apid, matrix_mdev->matrix.apm, AP_DEVICES) {
>>> +        apqn = AP_MKQID(apid, apqi);
>>> +        q = vfio_ap_find_queue(apqn);
>>> +        if (!q) {
>>> +            ret = -EADDRNOTAVAIL;
>>> +            goto rewind;
>>> +        }
>>> +        if (q->matrix_mdev) {
>>
>> If somebody assigns the same domain a second time, the assignment will
>> fail because the matrix_mdev will already have been associated with the
>> queue. I don't think it is appropriate to fail the assignment if the
> 
> It is usual to report a failure in the case the operation requested has 
> already be done.
> But we can do as you want. Any other opinion?
> 
>> q->matrix_mdev is the same as the input matrix_mdev. This should be
>> changed to:
>>
>>      if (q->matrix_mdev != matrix_mdev)
> 
> You surely want to say: add this, not change to this. ;)

Yes

> 
>>
> 
> Thanks for commenting,
> 
> Regards,
> Pierre
> 
>