linux-kernel - Re: [PATCH v10 02/16] s390/vfio-ap: use new AP bus interface to search for queue devices

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Date:   Tue, 29 Sep 2020 09:07:40 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ux.ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, mjrosato@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        fiuczy@...ux.ibm.com, frankja@...ux.ibm.com, david@...hat.com,
        imbrenda@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v10 02/16] s390/vfio-ap: use new AP bus interface to
 search for queue devices



On 9/24/20 10:27 PM, Halil Pasic wrote:
> On Fri, 21 Aug 2020 15:56:02 -0400
> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
>
>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>> @@ -26,43 +26,26 @@
>>   
>>   static int vfio_ap_mdev_reset_queues(struct mdev_device *mdev);
>>   
>> -static int match_apqn(struct device *dev, const void *data)
>> -{
>> -	struct vfio_ap_queue *q = dev_get_drvdata(dev);
>> -
>> -	return (q->apqn == *(int *)(data)) ? 1 : 0;
>> -}
>> -
>>   /**
>> - * 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))
>> +	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);
> Is this cast here safe? (I don't think it is.)

In the probe, we execute:
dev_set_drvdata(&queue->ap_dev.device, q);

I don't get any compile nor execution errors. Why wouldn't it be safe?

>
>> +	put_device(&queue->ap_dev.device);
>>   
>>   	return q;
>>   }