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

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Message-Id: <d7154477-8b87-71f8-1e15-ada53c765f61@linux.ibm.com>
Date:   Thu, 28 Mar 2019 17:06:06 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...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 28/03/2019 16:32, Tony Krowiak wrote:
> 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

...
>>>> +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.

:) OK


Regards,
Pierre

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