diff -r 23e3ab980622 -r 9b7b9f16dfd9 src/hotspot/share/prims/unsafe.cpp
--- a/src/hotspot/share/prims/unsafe.cpp	Tue Aug 20 10:46:23 2019 +0200
+++ b/src/hotspot/share/prims/unsafe.cpp	Tue Aug 20 10:11:53 2019 +0100
@@ -44,6 +44,7 @@
 #include "runtime/jniHandles.inline.hpp"
 #include "runtime/orderAccess.hpp"
 #include "runtime/reflection.hpp"
+#include "runtime/sharedRuntime.hpp"
 #include "runtime/thread.hpp"
 #include "runtime/threadSMR.hpp"
 #include "runtime/vm_version.hpp"
@@ -445,6 +446,46 @@
   }
 } UNSAFE_END
 
+UNSAFE_LEAF (void, Unsafe_WriteBack0(JNIEnv *env, jobject unsafe, jlong line)) {
+  assert(VM_Version::supports_data_cache_line_flush(), "should not get here");
+#ifdef ASSERT
+  if (TraceMemoryWriteback) {
+    tty->print_cr("Unsafe: writeback 0x%p", addr_from_java(line));
+  }
+#endif
+
+  assert(StubRoutines::data_cache_writeback() != NULL, "sanity");
+  (StubRoutines::DataCacheWriteback_stub())(addr_from_java(line));
+} UNSAFE_END
+
+static void doWriteBackSync0(bool is_pre)
+{
+  assert(StubRoutines::data_cache_writeback_sync() != NULL, "sanity");
+  (StubRoutines::DataCacheWritebackSync_stub())(is_pre);
+}
+
+UNSAFE_LEAF (void, Unsafe_WriteBackPreSync0(JNIEnv *env, jobject unsafe)) {
+  assert(VM_Version::supports_data_cache_line_flush(), "should not get here");
+#ifdef ASSERT
+  if (TraceMemoryWriteback) {
+      tty->print_cr("Unsafe: writeback pre-sync");
+  }
+#endif
+
+  doWriteBackSync0(true);
+} UNSAFE_END
+
+UNSAFE_LEAF (void, Unsafe_WriteBackPostSync0(JNIEnv *env, jobject unsafe)) {
+  assert(VM_Version::supports_data_cache_line_flush(), "should not get here");
+#ifdef ASSERT
+  if (TraceMemoryWriteback) {
+    tty->print_cr("Unsafe: writeback pre-sync");
+  }
+#endif
+
+  doWriteBackSync0(false);
+} UNSAFE_END
+
 ////// Random queries
 
 static jlong find_field_offset(jclass clazz, jstring name, TRAPS) {
@@ -1073,6 +1114,9 @@
 
     {CC "copyMemory0",        CC "(" OBJ "J" OBJ "JJ)V", FN_PTR(Unsafe_CopyMemory0)},
     {CC "copySwapMemory0",    CC "(" OBJ "J" OBJ "JJJ)V", FN_PTR(Unsafe_CopySwapMemory0)},
+    {CC "writeback0",         CC "(" "J" ")V",           FN_PTR(Unsafe_WriteBack0)},
+    {CC "writebackPreSync0",  CC "()V",                  FN_PTR(Unsafe_WriteBackPreSync0)},
+    {CC "writebackPostSync0", CC "()V",                  FN_PTR(Unsafe_WriteBackPostSync0)},
     {CC "setMemory0",         CC "(" OBJ "JJB)V",        FN_PTR(Unsafe_SetMemory0)},
 
     {CC "defineAnonymousClass0", CC "(" DAC_Args ")" CLS, FN_PTR(Unsafe_DefineAnonymousClass0)},