diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index a403d0f59122..d2f99079f619 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -2772,12 +2772,20 @@ static void vfio_ap_mdev_cfg_add(unsigned long *apm_add, unsigned long *aqm_add,
 	 * called.
 	 */
 	list_for_each_entry(matrix_mdev, &matrix_dev->mdev_list, node) {
+		/*
+		 * The mdevs_lock must be held in order to access fields
+		 * within matrix_mdev
+		 */
+		mutex_lock(&matrix_dev->mdevs_lock);
+
 		bitmap_and(matrix_mdev->apm_add,
 			   matrix_mdev->matrix.apm, apm_add, AP_DEVICES);
 		bitmap_and(matrix_mdev->aqm_add,
 			   matrix_mdev->matrix.aqm, aqm_add, AP_DOMAINS);
 		bitmap_and(matrix_mdev->adm_add,
 			   matrix_mdev->matrix.adm, adm_add, AP_DEVICES);
+
+		mutex_unlock(&matrix_dev->mdevs_lock);
 	}
 }