only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php
+++ b/core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php
@@ -127,6 +127,20 @@ class EntityAutocomplete extends Textfield {
     // Store the selection settings in the key/value store and pass a hashed key
     // in the route parameters.
     $selection_settings = isset($element['#selection_settings']) ? $element['#selection_settings'] : [];
+
+    $entity = isset($selection_settings['entity']) ? $selection_settings['entity'] : NULL;
+    if ($entity instanceof EntityInterface) {
+      // Don't serialise the entity, just pack the ID's.
+      $entity_info = [
+        'uuid' => $entity->uuid(),
+        'entity_type' => $entity->getEntityTypeId(),
+      ];
+      if (!$entity_info['uuid']) {
+        $entity_info['id'] = $entity->id();
+      }
+      $selection_settings['entity'] = $entity_info;
+    }
+
     $data = serialize($selection_settings) . $element['#target_type'] . $element['#selection_handler'];
     $selection_settings_key = Crypt::hmacBase64($data, Settings::getHashSalt());
 
only in patch2:
unchanged:
--- a/core/modules/system/src/Controller/EntityAutocompleteController.php
+++ b/core/modules/system/src/Controller/EntityAutocompleteController.php
@@ -7,6 +7,8 @@ use Drupal\Component\Utility\Tags;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Controller\ControllerBase;
 use Drupal\Core\Entity\EntityAutocompleteMatcher;
+use Drupal\Core\Entity\EntityRepositoryInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\KeyValueStore\KeyValueStoreInterface;
 use Drupal\Core\Site\Settings;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -100,10 +102,39 @@ class EntityAutocompleteController extends ControllerBase {
         throw new AccessDeniedHttpException();
       }
 
+      $entity_info = isset($selection_settings['entity']) ? $selection_settings['entity'] : NULL;
+      if (is_array($entity_info)) {
+        $selection_settings['entity'] = $this->loadEntityFromIds($entity_info);
+      }
+
       $matches = $this->matcher->getMatches($target_type, $selection_handler, $selection_settings, $typed_string);
     }
 
     return new JsonResponse($matches);
   }
 
+  /**
+   * Loads an entity from storage given entity ID's.
+   *
+   * @param array $entity_info
+   *   An array containing keys, where either uuid or ID is required:
+   *   - 'entity_type': Required. An entity type ID.
+   *   - 'uuid': Optional. An entity UUID.
+   *   - 'id': Optional. An entity ID.
+   *
+   * @return \Drupal\Core\Entity\EntityInterface|null
+   *   The entity loaded from provided ID's, or null if it does not exist.
+   */
+  protected function loadEntityFromIds(array $entity_info) {
+    $entity_type = $entity_info['entity_type'];
+    $uuid = !empty($entity_info['uuid']) ? $entity_info['uuid'] : NULL;
+    if ($uuid) {
+      return $this->entityManager()->loadEntityByUuid($entity_type, $uuid);
+    }
+    else {
+      return $this->entityManager()->getStorage($entity_type)
+        ->load($entity_info['id']);
+    }
+  }
+
 }