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Subject: Re: [PATCH v10 02/16] s390/vfio-ap: use new AP bus interface to
 search for queue devices
To:     Cornelia Huck <cohuck@redhat.com>
Cc:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, freude@linux.ibm.com, borntraeger@de.ibm.com,
        mjrosato@linux.ibm.com, pasic@linux.ibm.com,
        alex.williamson@redhat.com, kwankhede@nvidia.com,
        fiuczy@linux.ibm.com, frankja@linux.ibm.com, david@redhat.com,
        imbrenda@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com,
        kernel test robot <lkp@intel.com>
References: <20200821195616.13554-1-akrowiak@linux.ibm.com>
 <20200821195616.13554-3-akrowiak@linux.ibm.com>
 <20200825121334.0ff35d7a.cohuck@redhat.com>
 <b1c6bad8-3ec6-183c-3e35-9962e9c721c7@linux.ibm.com>
 <20200828101357.2ccbc39a.cohuck@redhat.com>
From:   Tony Krowiak <akrowiak@linux.ibm.com>
Message-ID: <d4faf910-ea86-bcda-13e1-544243477568@linux.ibm.com>
Date:   Fri, 28 Aug 2020 11:10:40 -0400
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On 8/28/20 4:13 AM, Cornelia Huck wrote:
> On Thu, 27 Aug 2020 10:24:07 -0400
> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
>
>> On 8/25/20 6:13 AM, Cornelia Huck wrote:
>>> On Fri, 21 Aug 2020 15:56:02 -0400
>>> Tony Krowiak<akrowiak@linux.ibm.com>  wrote:
>>>>    /**
>>>> - * vfio_ap_get_queue: Retrieve a queue with a specific APQN from a list
>>>> - * @matrix_mdev: the associated mediated matrix
>>>> + * vfio_ap_get_queue: Retrieve a queue with a specific APQN.
>>>>     * @apqn: The queue APQN
>>>>     *
>>>> - * Retrieve a queue with a specific APQN from the list of the
>>>> - * devices of the vfio_ap_drv.
>>>> - * Verify that the APID and the APQI are set in the matrix.
>>>> + * Retrieve a queue with a specific APQN from the AP queue devices attached to
>>>> + * the AP bus.
>>>>     *
>>>> - * Returns the pointer to the associated vfio_ap_queue
>>>> + * Returns the pointer to the vfio_ap_queue with the specified APQN, or NULL.
>>>>     */
>>>> -static struct vfio_ap_queue *vfio_ap_get_queue(
>>>> -					struct ap_matrix_mdev *matrix_mdev,
>>>> -					int apqn)
>>>> +static struct vfio_ap_queue *vfio_ap_get_queue(unsigned long apqn)
>>>>    {
>>>> +	struct ap_queue *queue;
>>>>    	struct vfio_ap_queue *q;
>>>> -	struct device *dev;
>>>>    
>>>> -	if (!test_bit_inv(AP_QID_CARD(apqn), matrix_mdev->matrix.apm))
>>>> -		return NULL;
>>>> -	if (!test_bit_inv(AP_QID_QUEUE(apqn), matrix_mdev->matrix.aqm))
>>> I think you should add some explanation to the patch description why
>>> testing the matrix bitmasks is not needed anymore.
>> As a result of this comment, I took a closer look at the code to
>> determine the reason for eliminating the matrix_mdev
>> parameter. The reason is because the code below (i.e., find the device
>> and get the driver data) was also repeated in the vfio_ap_irq_disable_apqn()
>> function, so I replaced it with a call to the function above; however, the
>> vfio_ap_irq_disable_apqn() function  does not have a reference to the
>> matrix_mdev, so I eliminated the matrix_mdev parameter. Note that the
>> vfio_ap_irq_disable_apqn() is called for each APQN assigned to a matrix
>> mdev, so there is no need to test the bitmasks there.
>>
>> The other place from which the function above is called is
>> the handle_pqap() function which does have a reference to the
>> matrix_mdev. In order to ensure the integrity of the instruction
>> being intercepted - i.e., PQAP(AQIC) enable/disable IRQ for aN
>> AP queue - the testing of the matrix bitmasks probably ought to
>> be performed, so it will be done there instead of in the
>> vfio_ap_get_queue() function above.
> Should you add a comment that vfio_ap_get_queue() assumes that the
> caller makes sure that this is only called for APQNs that are assigned
> to a matrix?

I suppose it wouldn't hurt.

>
>>
>>> +	queue = ap_get_qdev(apqn);
>>> +	if (!queue)
>>>    		return NULL;
>>>    
>>> -	dev = driver_find_device(&matrix_dev->vfio_ap_drv->driver, NULL,
>>> -				 &apqn, match_apqn);
>>> -	if (!dev)
>>> -		return NULL;
>>> -	q = dev_get_drvdata(dev);
>>> -	q->matrix_mdev = matrix_mdev;
>>> -	put_device(dev);
>>> +	q = dev_get_drvdata(&queue->ap_dev.device);
>>> +	put_device(&queue->ap_dev.device);
>>>    
>>>    	return q;
>>>    }
>>> (...)
>>>