diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index cb3e4f7671be..cda1d216ee38 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -155,6 +155,24 @@ static int vfio_ap_mdev_verify_no_sharing(struct ap_matrix_mdev *matrix_mdev)
 	return 0;
 }
 
+/*
+ * vfio_ap_mdev_update_crycb
+ *
+ * @matrix_mdev: the mediated matrix device
+ *
+ * Updates the AP matrix in the guest's CRYCB from the masks configured for the
+ * mediated matrix device via its sysfs interfaces.
+ */
+static void vfio_ap_mdev_update_crycb(struct ap_matrix_mdev *matrix_mdev)
+{
+	if (matrix_mdev->kvm) {
+		kvm_arch_crypto_set_masks(matrix_mdev->kvm,
+					  matrix_mdev->matrix.apm,
+					  matrix_mdev->matrix.aqm,
+					  matrix_mdev->matrix.adm);
+	}
+}
+
 /**
  * assign_adapter_store
  *
@@ -196,10 +214,6 @@ static ssize_t assign_adapter_store(struct device *dev,
 	struct mdev_device *mdev = mdev_from_dev(dev);
 	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
 
-	/* If the guest is running, disallow assignment of adapter */
-	if (matrix_mdev->kvm)
-		return -EBUSY;
-
 	ret = kstrtoul(buf, 0, &apid);
 	if (ret)
 		return ret;
@@ -214,16 +228,12 @@ static ssize_t assign_adapter_store(struct device *dev,
 	 */
 	mutex_lock(&matrix_dev->lock);
 
-	ret = vfio_ap_mdev_verify_queues_reserved_for_apid(matrix_mdev, apid);
-	if (ret)
-		goto done;
-
 	set_bit_inv(apid, matrix_mdev->matrix.apm);
 
 	ret = ap_apqn_in_matrix_owned_by_def_drv(matrix_mdev->matrix.apm,
 						 matrix_mdev->matrix.aqm);
 
-	/* If any APQN is reserved for used by the default drivers */
+	/* If any APQN is owned by the default drivers */
 	ret = (ret == 1) ? -EADDRNOTAVAIL : ret;
 	if (ret)
 		goto error;
@@ -232,6 +242,7 @@ static ssize_t assign_adapter_store(struct device *dev,
 	if (ret)
 		goto error;
 
+	vfio_ap_mdev_update_crycb(matrix_mdev);
 	ret = count;
 	goto done;
 
@@ -270,10 +281,6 @@ static ssize_t unassign_adapter_store(struct device *dev,
 	struct mdev_device *mdev = mdev_from_dev(dev);
 	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
 
-	/* If the guest is running, disallow un-assignment of adapter */
-	if (matrix_mdev->kvm)
-		return -EBUSY;
-
 	ret = kstrtoul(buf, 0, &apid);
 	if (ret)
 		return ret;
@@ -283,6 +290,7 @@ static ssize_t unassign_adapter_store(struct device *dev,
 
 	mutex_lock(&matrix_dev->lock);
 	clear_bit_inv((unsigned long)apid, matrix_mdev->matrix.apm);
+	vfio_ap_mdev_update_crycb(matrix_mdev);
 	mutex_unlock(&matrix_dev->lock);
 
 	return count;
@@ -331,10 +339,6 @@ static ssize_t assign_domain_store(struct device *dev,
 	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
 	unsigned long max_apqi = matrix_mdev->matrix.aqm_max;
 
-	/* If the guest is running, disallow assignment of domain */
-	if (matrix_mdev->kvm)
-		return -EBUSY;
-
 	ret = kstrtoul(buf, 0, &apqi);
 	if (ret)
 		return ret;
@@ -355,12 +359,13 @@ static ssize_t assign_domain_store(struct device *dev,
 
 	ret = vfio_ap_mdev_verify_no_sharing(matrix_mdev);
 	if (ret)
-		goto share_err;
+		goto error;
 
+	vfio_ap_mdev_update_crycb(matrix_mdev);
 	ret = count;
 	goto done;
 
-share_err:
+error:
 	clear_bit_inv(apqi, matrix_mdev->matrix.aqm);
 done:
 	mutex_unlock(&matrix_dev->lock);
@@ -396,10 +401,6 @@ static ssize_t unassign_domain_store(struct device *dev,
 	struct mdev_device *mdev = mdev_from_dev(dev);
 	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
 
-	/* If the guest is running, disallow un-assignment of domain */
-	if (matrix_mdev->kvm)
-		return -EBUSY;
-
 	ret = kstrtoul(buf, 0, &apqi);
 	if (ret)
 		return ret;
@@ -409,6 +410,7 @@ static ssize_t unassign_domain_store(struct device *dev,
 
 	mutex_lock(&matrix_dev->lock);
 	clear_bit_inv((unsigned long)apqi, matrix_mdev->matrix.aqm);
+	vfio_ap_mdev_update_crycb(matrix_mdev);
 	mutex_unlock(&matrix_dev->lock);
 
 	return count;
@@ -440,10 +442,6 @@ static ssize_t assign_control_domain_store(struct device *dev,
 	struct mdev_device *mdev = mdev_from_dev(dev);
 	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
 
-	/* If the guest is running, disallow assignment of control domain */
-	if (matrix_mdev->kvm)
-		return -EBUSY;
-
 	ret = kstrtoul(buf, 0, &id);
 	if (ret)
 		return ret;
@@ -451,13 +449,16 @@ static ssize_t assign_control_domain_store(struct device *dev,
 	if (id > matrix_mdev->matrix.adm_max)
 		return -ENODEV;
 
-	/* Set the bit in the ADM (bitmask) corresponding to the AP control
-	 * domain number (id). The bits in the mask, from most significant to
-	 * least significant, correspond to IDs 0 up to the one less than the
-	 * number of control domains that can be assigned.
+	/*
+	 * Set the bits in the ADM (bitmask) corresponding to the AP control
+	 * domain numbers in dommask. The bits in the mask, from left to right,
+	 * correspond to IDs 0 up to the one less than the number of control
+	 * domains that can be assigned.
+	 *
 	 */
 	mutex_lock(&matrix_dev->lock);
 	set_bit_inv(id, matrix_mdev->matrix.adm);
+	vfio_ap_mdev_update_crycb(matrix_mdev);
 	mutex_unlock(&matrix_dev->lock);
 
 	return count;
@@ -490,10 +491,6 @@ static ssize_t unassign_control_domain_store(struct device *dev,
 	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
 	unsigned long max_domid =  matrix_mdev->matrix.adm_max;
 
-	/* If the guest is running, disallow un-assignment of control domain */
-	if (matrix_mdev->kvm)
-		return -EBUSY;
-
 	ret = kstrtoul(buf, 0, &domid);
 	if (ret)
 		return ret;
@@ -502,6 +499,7 @@ static ssize_t unassign_control_domain_store(struct device *dev,
 
 	mutex_lock(&matrix_dev->lock);
 	clear_bit_inv(domid, matrix_mdev->matrix.adm);
+	vfio_ap_mdev_update_crycb(matrix_mdev);
 	mutex_unlock(&matrix_dev->lock);
 
 	return count;
