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:   Fri, 28 Aug 2020 10:13:57 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Tony Krowiak <akrowiak@...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,
        mjrosato@...ux.ibm.com, pasic@...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 Thu, 27 Aug 2020 10:24:07 -0400
Tony Krowiak <akrowiak@...ux.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@...ux.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?

> 
> 
> > +	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;
> >   }
> > (...)
> >  
>