s390/vfio-ap: add status attribute to AP queue device's sysfs dir

This patch adds a sysfs 'status' attribute to a queue device when it is
bound to the vfio_ap device driver. The field displays a string indicating
the status of the queue device:

Status String:  Indicates:
-------------   ---------
"assigned"      the queue is assigned to an mdev, but is not in use by a
                KVM guest.
"in use"        the queue is assigned to an mdev and is in use by a KVM
                guest.
"unassigned"    the queue is not assigned to an mdev.

The status string will be displayed by the 'lszcrypt' command if the queue
device is bound to the vfio_ap device driver.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
[akrowiak@linux.ibm.com: added check for queue in use by guest]
Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

drivers/s390/crypto/vfio_ap_drv.c

@@ -17,6 +17,9 @@
 
 #define VFIO_AP_ROOT_NAME "vfio_ap"
 #define VFIO_AP_DEV_NAME "matrix"
+#define AP_QUEUE_ASSIGNED "assigned"
+#define AP_QUEUE_UNASSIGNED "unassigned"
+#define AP_QUEUE_IN_USE "in use"
 
 MODULE_AUTHOR("IBM Corporation");
 MODULE_DESCRIPTION("VFIO AP device driver, Copyright IBM Corp. 2018");
@@ -41,26 +44,95 @@ static struct ap_device_id ap_queue_ids[] = {
 
 MODULE_DEVICE_TABLE(vfio_ap, ap_queue_ids);
 
+static struct ap_matrix_mdev *vfio_ap_mdev_for_queue(struct vfio_ap_queue *q)
+{
+	struct ap_matrix_mdev *matrix_mdev;
+	unsigned long apid = AP_QID_CARD(q->apqn);
+	unsigned long apqi = AP_QID_QUEUE(q->apqn);
+
+	list_for_each_entry(matrix_mdev, &matrix_dev->mdev_list, node) {
+		if (test_bit_inv(apid, matrix_mdev->matrix.apm) &&
+		    test_bit_inv(apqi, matrix_mdev->matrix.aqm))
+			return matrix_mdev;
+	}
+
+	return NULL;
+}
+
+static ssize_t status_show(struct device *dev,
+			   struct device_attribute *attr,
+			   char *buf)
+{
+	ssize_t nchars = 0;
+	struct vfio_ap_queue *q;
+	struct ap_matrix_mdev *matrix_mdev;
+	struct ap_device *apdev = to_ap_dev(dev);
+
+	mutex_lock(&matrix_dev->lock);
+	q = dev_get_drvdata(&apdev->device);
+	matrix_mdev = vfio_ap_mdev_for_queue(q);
+
+	if (matrix_mdev) {
+		if (matrix_mdev->kvm)
+			nchars = scnprintf(buf, PAGE_SIZE, "%s\n",
+					   AP_QUEUE_IN_USE);
+		else
+			nchars = scnprintf(buf, PAGE_SIZE, "%s\n",
+					   AP_QUEUE_ASSIGNED);
+	} else {
+		nchars = scnprintf(buf, PAGE_SIZE, "%s\n",
+				   AP_QUEUE_UNASSIGNED);
+	}
+
+	mutex_unlock(&matrix_dev->lock);
+
+	return nchars;
+}
+
+static DEVICE_ATTR_RO(status);
+
+static struct attribute *vfio_queue_attrs[] = {
+	&dev_attr_status.attr,
+	NULL,
+};
+
+static const struct attribute_group vfio_queue_attr_group = {
+	.attrs = vfio_queue_attrs,
+};
+
 /**
  * vfio_ap_queue_dev_probe: Allocate a vfio_ap_queue structure and associate it
  *			    with the device as driver_data.
  *
  * @apdev: the AP device being probed
  *
- * Return: returns 0 if the probe succeeded; otherwise, returns -ENOMEM if
+ * Return: returns 0 if the probe succeeded; otherwise, returns an error if
- *	   storage could not be allocated for a vfio_ap_queue object.
+ *	   storage could not be allocated for a vfio_ap_queue object or the
+ *	   sysfs 'status' attribute could not be created for the queue device.
  */
 static int vfio_ap_queue_dev_probe(struct ap_device *apdev)
 {
+	int ret;
 	struct vfio_ap_queue *q;
 
 	q = kzalloc(sizeof(*q), GFP_KERNEL);
 	if (!q)
 		return -ENOMEM;
+
+	mutex_lock(&matrix_dev->lock);
 	dev_set_drvdata(&apdev->device, q);
 	q->apqn = to_ap_queue(&apdev->device)->qid;
 	q->saved_isc = VFIO_AP_ISC_INVALID;
-	return 0;
+
+	ret = sysfs_create_group(&apdev->device.kobj, &vfio_queue_attr_group);
+	if (ret) {
+		dev_set_drvdata(&apdev->device, NULL);
+		kfree(q);
+	}
+
+	mutex_unlock(&matrix_dev->lock);
+
+	return ret;
 }
 
 /**
@@ -75,6 +147,7 @@ static void vfio_ap_queue_dev_remove(struct ap_device *apdev)
 	struct vfio_ap_queue *q;
 
 	mutex_lock(&matrix_dev->lock);
+	sysfs_remove_group(&apdev->device.kobj, &vfio_queue_attr_group);
 	q = dev_get_drvdata(&apdev->device);
 	vfio_ap_mdev_reset_queue(q, 1);
 	dev_set_drvdata(&apdev->device, NULL);