diff --git a/jikesrvm/rvm/src/org/jikesrvm/VMExt.java b/jikesrvm/rvm/src/org/jikesrvm/VMExt.java
new file mode 100644
index 00000000..8de7ad5b
--- /dev/null
+++ b/jikesrvm/rvm/src/org/jikesrvm/VMExt.java
@@ -0,0 +1,20 @@
+package org.jikesrvm;
+
+import org.jikesrvm.scheduler.RVMThread;
+import org.vmmagic.pragma.Entrypoint;
+
+public class VMExt {
+    @Entrypoint
+    public static int enterVM() {
+        RVMThread cur = RVMThread.getCurrentThread();
+        int old = cur.getExecStatus();
+        cur.setExecStatus(RVMThread.IN_JAVA);
+        return old;
+    }
+
+    @Entrypoint
+    public static void leaveVM(int status) {
+        RVMThread cur = RVMThread.getCurrentThread();
+        cur.setExecStatus(status);
+    }
+}
diff --git a/jikesrvm/rvm/src/org/jikesrvm/runtime/Entrypoints.java b/jikesrvm/rvm/src/org/jikesrvm/runtime/Entrypoints.java
index 0e7d4489..78fba419 100644
--- a/jikesrvm/rvm/src/org/jikesrvm/runtime/Entrypoints.java
+++ b/jikesrvm/rvm/src/org/jikesrvm/runtime/Entrypoints.java
@@ -32,6 +32,10 @@ public class Entrypoints {
                   "(Lorg/jikesrvm/scheduler/RVMThread;Lorg/vmmagic/unboxed/Address;ZZ)V");
   public static final NormalMethod scanBootImageMethod =
           getMethod(org.jikesrvm.mm.mminterface.RustScanning.class, "scanBootImage", "(Lorg/vmmagic/unboxed/Address;)V");
+  public static final NormalMethod enterVMMethod =
+          getMethod(org.jikesrvm.VMExt.class, "enterVM", "()I");
+  public static final NormalMethod leaveVMMethod =
+          getMethod(org.jikesrvm.VMExt.class, "leaveVM", "(I)V");
 
   // The usual causes for getField/Method() to fail are:
   //  1. you misspelled the class name, member name, or member signature
diff --git a/mmtk/src/api.rs b/mmtk/src/api.rs
index f8ba8c5b..1c236efb 100644
--- a/mmtk/src/api.rs
+++ b/mmtk/src/api.rs
@@ -159,13 +159,25 @@ pub extern "C" fn add_phantom_candidate(reff: ObjectReference, referent: ObjectR
 }
 
 #[no_mangle]
-pub extern "C" fn harness_begin(tls: OpaquePointer) {
-    memory_manager::harness_begin(&SINGLETON, tls)
+pub extern "C" fn harness_begin(id: usize) {
+    unsafe {
+        let thread_from_id = VMCollection::thread_from_id(id);
+        let tls = OpaquePointer::from_address(thread_from_id);
+        let st = JikesRVM::enter_vm(tls);
+        memory_manager::harness_begin(&SINGLETON, tls);
+        JikesRVM::leave_vm(tls, st);
+    }
 }
 
 #[no_mangle]
-pub extern "C" fn harness_end(tls: OpaquePointer) {
-    memory_manager::harness_end(&SINGLETON)
+pub extern "C" fn harness_end(id: usize) {
+    unsafe {
+        let thread_from_id = VMCollection::thread_from_id(id);
+        let tls = OpaquePointer::from_address(thread_from_id);
+        let st = JikesRVM::enter_vm(tls);
+        memory_manager::harness_end(&SINGLETON);
+        JikesRVM::leave_vm(tls, st);
+    }
 }
 
 #[no_mangle]
diff --git a/mmtk/src/lib.rs b/mmtk/src/lib.rs
index d205ae75..1ca45eb6 100644
--- a/mmtk/src/lib.rs
+++ b/mmtk/src/lib.rs
@@ -8,6 +8,7 @@ extern crate lazy_static;
 extern crate log;
 
 use mmtk::util::address::Address;
+use mmtk::util::OpaquePointer;
 use mmtk::TraceLocal;
 use mmtk::vm::VMBinding;
 use mmtk::MMTK;
@@ -77,6 +78,18 @@ impl JikesRVM {
             jtoc_call!(TEST3_METHOD_OFFSET, BOOT_THREAD, input1, input2, input3, input4)
         }
     }
+
+    pub fn enter_vm(tls: OpaquePointer) -> i32 {
+        unsafe {
+            jtoc_call!(ENTER_VM_METHOD_OFFSET, tls) as i32
+        }
+    }
+
+    pub fn leave_vm(tls: OpaquePointer, status: i32) {
+        unsafe {
+            jtoc_call!(LEAVE_VM_METHOD_OFFSET, tls, status);
+        }
+    }
 }
 
 lazy_static! {
diff --git a/repos/jikesrvm b/repos/jikesrvm
index 67dadebb..c4b7938d 160000
--- a/repos/jikesrvm
+++ b/repos/jikesrvm
@@ -1 +1 @@
-Subproject commit 67dadebb060ed48687dabf7e30805ee70a810686
+Subproject commit c4b7938d0d2cddd9ea5021941fd0a7eaa49dbf76