diff -r c749ecf599c0 -r 3f3dc00a69a5 src/hotspot/share/prims/unsafe.cpp
--- a/src/hotspot/share/prims/unsafe.cpp	Thu Jun 20 14:09:22 2019 +0100
+++ b/src/hotspot/share/prims/unsafe.cpp	Mon Jun 24 11:37:56 2019 -0700
@@ -149,6 +149,25 @@
 ///// Data read/writes on the Java heap and in native (off-heap) memory
 
 /**
+ * Helper class to wrap memory accesses in JavaThread::doing_unsafe_access()
+ */
+class GuardUnsafeAccess {
+  JavaThread* _thread;
+
+public:
+  GuardUnsafeAccess(JavaThread* thread) : _thread(thread) {
+    // native/off-heap access which may raise SIGBUS if accessing
+    // memory mapped file data in a region of the file which has
+    // been truncated and is now invalid.
+    _thread->set_doing_unsafe_access(true);
+  }
+
+  ~GuardUnsafeAccess() {
+    _thread->set_doing_unsafe_access(false);
+  }
+};
+
+/**
  * Helper class for accessing memory.
  *
  * Normalizes values and wraps accesses in
@@ -189,25 +208,6 @@
     return x != 0;
   }
 
-  /**
-   * Helper class to wrap memory accesses in JavaThread::doing_unsafe_access()
-   */
-  class GuardUnsafeAccess {
-    JavaThread* _thread;
-
-  public:
-    GuardUnsafeAccess(JavaThread* thread) : _thread(thread) {
-      // native/off-heap access which may raise SIGBUS if accessing
-      // memory mapped file data in a region of the file which has
-      // been truncated and is now invalid
-      _thread->set_doing_unsafe_access(true);
-    }
-
-    ~GuardUnsafeAccess() {
-      _thread->set_doing_unsafe_access(false);
-    }
-  };
-
 public:
   MemoryAccess(JavaThread* thread, jobject obj, jlong offset)
     : _thread(thread), _obj(JNIHandles::resolve(obj)), _offset((ptrdiff_t)offset) {
@@ -399,8 +399,14 @@
 
   void* src = index_oop_from_field_offset_long(srcp, srcOffset);
   void* dst = index_oop_from_field_offset_long(dstp, dstOffset);
-
-  Copy::conjoint_memory_atomic(src, dst, sz);
+  {
+    GuardUnsafeAccess guard(thread);
+    if (StubRoutines::unsafe_arraycopy() != NULL) {
+      StubRoutines::UnsafeArrayCopy_stub()(src, dst, sz);
+    } else {
+      Copy::conjoint_memory_atomic(src, dst, sz);
+    }
+  }
 } UNSAFE_END
 
 // This function is a leaf since if the source and destination are both in native memory
@@ -416,7 +422,11 @@
     address src = (address)srcOffset;
     address dst = (address)dstOffset;
 
-    Copy::conjoint_swap(src, dst, sz, esz);
+    {
+      JavaThread* thread = JavaThread::thread_from_jni_environment(env);
+      GuardUnsafeAccess guard(thread);
+      Copy::conjoint_swap(src, dst, sz, esz);
+    }
   } else {
     // At least one of src/dst are on heap, transition to VM to access raw pointers
 
@@ -427,7 +437,10 @@
       address src = (address)index_oop_from_field_offset_long(srcp, srcOffset);
       address dst = (address)index_oop_from_field_offset_long(dstp, dstOffset);
 
-      Copy::conjoint_swap(src, dst, sz, esz);
+      {
+        GuardUnsafeAccess guard(thread);
+        Copy::conjoint_swap(src, dst, sz, esz);
+      }
     } JVM_END
   }
 } UNSAFE_END