Implement memory barriers

xtoskrnl/includes/amd64/ari.h

@@ -63,6 +63,10 @@ XTCDECL
 VOID
 ArLoadTaskRegister(USHORT Source);
 
+XTCDECL
+VOID
+ArMemoryBarrier();
+
 XTCDECL
 ULONG_PTR
 ArReadControlRegister(IN USHORT ControlRegister);
@@ -87,6 +91,10 @@ XTCDECL
 ULONGLONG
 ArReadTimeStampCounter();
 
+XTCDECL
+VOID
+ArReadWriteBarrier();
+
 XTAPI
 VOID
 ArSetGdtEntryBase(IN PKGDTENTRY Gdt,