Re: [PATCH v3 4/9] s390: ap: tools to find a queue with a specific APQN

Tony Krowiak
2019-02-15T22:13:21Z

On 2/14/19 8:51 AM, Pierre Morel wrote:
> We need to find the queue with a specific APQN during the
> handling of the interception of the PQAP/AQIC instruction.
>
> To handle the AP associated device reference count we keep
> track of it in the vfio_ap_queue until we put the device.
>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
> drivers/s390/crypto/vfio_ap_ops.c | 54 +++++++++++++++++++++++++++++++++++
> drivers/s390/crypto/vfio_ap_private.h | 1 +
> 2 files changed, 55 insertions(+)
>
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index 900b9cf..2a52c9b 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -24,6 +24,60 @@
> #define VFIO_AP_MDEV_TYPE_HWVIRT "passthrough"
> #define VFIO_AP_MDEV_NAME_HWVIRT "VFIO AP Passthrough Device"
>
> +/**
> + * vfio_ap_check_apqn: check if a ap_queue is of a given APQN
> + *
> + * Returns 1 if we have a match.
> + * Otherwise returns 0.
> + */
> +static int vfio_ap_check_apqn(struct device *dev, void *data)
> +{
> + struct vfio_ap_queue *q = dev_get_drvdata(dev);
> +
> + return (q->apqn == *(int *)data);
> +}
> +
> +/**
> + * 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 associated to the vfio_ap_driver.
> + *
> + * The vfio_ap_queue has been already associated with the device
> + * during the probe.
> + * Store the associated device for reference counting
> + *
> + * Returns the pointer to the associated vfio_ap_queue
> + */
> +static __attribute__((unused))
> + struct vfio_ap_queue *vfio_ap_get_queue(int apqn)

I think you should change this signature for the reasons I stated
below:

struct device *vfio_ap_get_queue_dev(int apqn)

> +{
> + struct device *dev;
> + struct vfio_ap_queue *q;
> +
> + dev = driver_find_device(&matrix_dev->vfio_ap_drv->driver, NULL, &apqn,
> + vfio_ap_check_apqn);
> + if (!dev)
> + return NULL;
> + q = dev_get_drvdata(dev);
> + q->dev = dev;

Why store the device with the vfio_ap_queue object? Why not just return
the device. The caller can get the vfio_ap_queue from the device's
driver data. It seems the only reason for the 'dev' field is to
temporarily hold a ref to the device so it can be put later. Why not
just put the device.

> + return q;
> +}
> +
> +/**
> + * vfio_ap_put_queue: lower device reference count for a queue
> + * @q: The queue
> + *
> + * put the associated device
> + *
> + */
> +static __attribute__((unused)) void vfio_ap_put_queue(struct vfio_ap_queue *q)
> +{
> + put_device(q->dev);
> + q->dev = NULL;
> +}

I would get rid of this function. If you take my suggestion above, you
can just call the put_device() directly. There will be no need for
this superfluous 'dev' field.

> +
> static void vfio_ap_matrix_init(struct ap_config_info *info,
> struct ap_matrix *matrix)
> {
> diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
> index 8836f01..081f0d7 100644
> --- a/drivers/s390/crypto/vfio_ap_private.h
> +++ b/drivers/s390/crypto/vfio_ap_private.h
> @@ -87,6 +87,7 @@ extern int vfio_ap_mdev_register(void);
> extern void vfio_ap_mdev_unregister(void);
>
> struct vfio_ap_queue {
> + struct device *dev;

No need for this as per my comments above.

> int apqn;
> };
> #endif /* _VFIO_AP_PRIVATE_H_ */
>