diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index bc8669b5c304..7c34fdaa2a27 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -873,48 +873,68 @@ static void vfio_ap_mdev_remove(struct mdev_device *mdev)
 	vfio_put_device(&matrix_mdev->vdev);
 }
 
-#define MDEV_SHARING_ERR "Userspace may not re-assign queue %02lx.%04lx " \
-			 "already assigned to %s"
+#define MDEV_SHARING_ERR "Userspace may not assign queue %02lx.%04lx to mdev: already assigned to %s"
 
-static void vfio_ap_mdev_log_sharing_err(struct ap_matrix_mdev *matrix_mdev,
-					 unsigned long *apm,
-					 unsigned long *aqm)
+#define MDEV_IN_USE_ERR "Can not reserve queue %02lx.%04lx for host driver: in use by mdev"
+
+static void vfio_ap_mdev_log_sharing_err(struct ap_matrix_mdev *assignee,
+					 struct ap_matrix_mdev *assigned_to,
+					 unsigned long *apm, unsigned long *aqm)
+{
+	unsigned long apid, apqi;
+
+	for_each_set_bit_inv(apid, apm, AP_DEVICES) {
+		for_each_set_bit_inv(apqi, aqm, AP_DOMAINS) {
+			dev_warn(mdev_dev(assignee->mdev), MDEV_SHARING_ERR,
+				 apid, apqi, dev_name(mdev_dev(assigned_to->mdev)));
+		}
+	}
+}
+
+static void vfio_ap_mdev_log_in_use_err(struct ap_matrix_mdev *assignee,
+					unsigned long *apm, unsigned long *aqm)
 {
 	unsigned long apid, apqi;
-	const struct device *dev = mdev_dev(matrix_mdev->mdev);
-	const char *mdev_name = dev_name(dev);
 
-	for_each_set_bit_inv(apid, apm, AP_DEVICES)
-		for_each_set_bit_inv(apqi, aqm, AP_DOMAINS)
-			dev_warn(dev, MDEV_SHARING_ERR, apid, apqi, mdev_name);
+	for_each_set_bit_inv(apid, apm, AP_DEVICES) {
+		for_each_set_bit_inv(apqi, aqm, AP_DOMAINS) {
+			dev_warn(mdev_dev(assignee->mdev), MDEV_IN_USE_ERR,
+				 apid, apqi);
+		}
+	}
 }
 
 /**
  * vfio_ap_mdev_verify_no_sharing - verify APQNs are not shared by matrix mdevs
  *
+ * @assignee: the matrix mdev to which @mdev_apm and @mdev_aqm are being
+ *            assigned; or, NULL if this function was called by the AP bus
+ *            driver in_use callback to verify none of the APQNs being reserved
+ *            for the host device driver are in use by a vfio_ap mediated device
  * @mdev_apm: mask indicating the APIDs of the APQNs to be verified
  * @mdev_aqm: mask indicating the APQIs of the APQNs to be verified
  *
- * Verifies that each APQN derived from the Cartesian product of a bitmap of
- * AP adapter IDs and AP queue indexes is not configured for any matrix
- * mediated device. AP queue sharing is not allowed.
+ * Verifies that each APQN derived from the Cartesian product of APIDs
+ * represented by the bits set in @mdev_apm and the APQIs of the bits set in
+ * @mdev_aqm is not assigned to a mediated device other than the mdev to which
+ * the APQN is being assigned (@assignee). AP queue sharing is not allowed.
  *
  * Return: 0 if the APQNs are not shared; otherwise return -EADDRINUSE.
  */
-static int vfio_ap_mdev_verify_no_sharing(unsigned long *mdev_apm,
+static int vfio_ap_mdev_verify_no_sharing(struct ap_matrix_mdev *assignee,
+					  unsigned long *mdev_apm,
 					  unsigned long *mdev_aqm)
 {
-	struct ap_matrix_mdev *matrix_mdev;
+	struct ap_matrix_mdev *assigned_to;
 	DECLARE_BITMAP(apm, AP_DEVICES);
 	DECLARE_BITMAP(aqm, AP_DOMAINS);
 
-	list_for_each_entry(matrix_mdev, &matrix_dev->mdev_list, node) {
+	list_for_each_entry(assigned_to, &matrix_dev->mdev_list, node) {
 		/*
-		 * If the input apm and aqm are fields of the matrix_mdev
-		 * object, then move on to the next matrix_mdev.
+		 * If the mdev to which the mdev_apm and mdev_aqm is being
+		 * assigned is the same as the mdev being verified
 		 */
-		if (mdev_apm == matrix_mdev->matrix.apm &&
-		    mdev_aqm == matrix_mdev->matrix.aqm)
+		if (assignee == assigned_to)
 			continue;
 
 		memset(apm, 0, sizeof(apm));
@@ -924,15 +944,22 @@ static int vfio_ap_mdev_verify_no_sharing(unsigned long *mdev_apm,
 		 * We work on full longs, as we can only exclude the leftover
 		 * bits in non-inverse order. The leftover is all zeros.
 		 */
-		if (!bitmap_and(apm, mdev_apm, matrix_mdev->matrix.apm,
-				AP_DEVICES))
+		if (!bitmap_and(apm, mdev_apm, assigned_to->matrix.apm,
+				AP_DEVICES)) {
 			continue;
+		}
 
-		if (!bitmap_and(aqm, mdev_aqm, matrix_mdev->matrix.aqm,
-				AP_DOMAINS))
+		if (!bitmap_and(aqm, mdev_aqm, assigned_to->matrix.aqm,
+				AP_DOMAINS)) {
 			continue;
+		}
 
-		vfio_ap_mdev_log_sharing_err(matrix_mdev, apm, aqm);
+		if (assignee) {
+			vfio_ap_mdev_log_sharing_err(assignee, assigned_to,
+						     apm, aqm);
+		} else {
+			vfio_ap_mdev_log_in_use_err(assigned_to, apm, aqm);
+		}
 
 		return -EADDRINUSE;
 	}
@@ -961,7 +988,8 @@ static int vfio_ap_mdev_validate_masks(struct ap_matrix_mdev *matrix_mdev)
 					       matrix_mdev->matrix.aqm))
 		return -EADDRNOTAVAIL;
 
-	return vfio_ap_mdev_verify_no_sharing(matrix_mdev->matrix.apm,
+	return vfio_ap_mdev_verify_no_sharing(matrix_mdev,
+					      matrix_mdev->matrix.apm,
 					      matrix_mdev->matrix.aqm);
 }
 
@@ -2516,7 +2544,7 @@ int vfio_ap_mdev_resource_in_use(unsigned long *apm, unsigned long *aqm)
 
 	mutex_lock(&matrix_dev->guests_lock);
 	mutex_lock(&matrix_dev->mdevs_lock);
-	ret = vfio_ap_mdev_verify_no_sharing(apm, aqm);
+	ret = vfio_ap_mdev_verify_no_sharing(NULL, apm, aqm);
 	mutex_unlock(&matrix_dev->mdevs_lock);
 	mutex_unlock(&matrix_dev->guests_lock);
 
