diff -r 2cb46eb4ed94 -r e5872950c9a3 src/cpu/base.cc
--- a/src/cpu/base.cc	Mon Aug 20 15:06:52 2012 +0100
+++ b/src/cpu/base.cc	Mon Aug 20 15:34:26 2012 +0100
@@ -413,17 +413,21 @@
         MasterPort *new_dtb_port = newTC->getDTBPtr()->getMasterPort();
 
         // Move over any table walker ports if they exist
-        if (new_itb_port && !new_itb_port->isConnected()) {
+        if (new_itb_port) {
+            assert(!new_itb_port->isConnected());
             assert(old_itb_port);
+            assert(old_itb_port->isConnected());
             SlavePort &slavePort = old_itb_port->getSlavePort();
+            old_itb_port->unbind();
             new_itb_port->bind(slavePort);
-            old_itb_port->unBind();
         }
-        if (new_dtb_port && !new_dtb_port->isConnected()) {
+        if (new_dtb_port) {
+            assert(!new_dtb_port->isConnected());
             assert(old_dtb_port);
+            assert(old_dtb_port->isConnected());
             SlavePort &slavePort = old_dtb_port->getSlavePort();
+            old_dtb_port->unbind();
             new_dtb_port->bind(slavePort);
-            old_dtb_port->unBind();
         }
 
         // Checker whether or not we have to transfer CheckerCPU
@@ -441,17 +445,21 @@
                 newChecker->getDTBPtr()->getMasterPort();
 
             // Move over any table walker ports if they exist for checker
-            if (new_checker_itb_port && !new_checker_itb_port->isConnected()) {
+            if (new_checker_itb_port) {
+                assert(!new_checker_itb_port->isConnected());
                 assert(old_checker_itb_port);
-                SlavePort &slavePort = old_checker_itb_port->getSlavePort();;
+                assert(old_checker_itb_port->isConnected());
+                SlavePort &slavePort = old_checker_itb_port->getSlavePort();
+                old_checker_itb_port->unbind();
                 new_checker_itb_port->bind(slavePort);
-                old_checker_itb_port->unBind();
             }
-            if (new_checker_dtb_port && !new_checker_dtb_port->isConnected()) {
+            if (new_checker_dtb_port) {
+                assert(!new_checker_dtb_port->isConnected());
                 assert(old_checker_dtb_port);
-                SlavePort &slavePort = old_checker_dtb_port->getSlavePort();;
+                assert(old_checker_dtb_port->isConnected());
+                SlavePort &slavePort = old_checker_dtb_port->getSlavePort();
+                old_checker_dtb_port->unbind();
                 new_checker_dtb_port->bind(slavePort);
-                old_checker_dtb_port->unBind();
             }
         }
     }
@@ -468,18 +476,21 @@
             schedule(profileEvent, curTick());
     }
 
-    // Connect new CPU to old CPU's memory only if new CPU isn't
-    // connected to anything.  Also connect old CPU's memory to new
-    // CPU.
-    if (!getInstPort().isConnected()) {
-        getInstPort().bind(oldCPU->getInstPort().getSlavePort());
-        oldCPU->getInstPort().unBind();
-    }
+    // All CPUs have an instruction and a data port, and the new CPU's
+    // ports are dangling while the old CPU has its ports connected
+    // already. Unbind the old CPU and then bind the ports of the one
+    // we are switching to.
+    assert(!getInstPort().isConnected());
+    assert(oldCPU->getInstPort().isConnected());
+    SlavePort &inst_peer_port = oldCPU->getInstPort().getSlavePort();
+    oldCPU->getInstPort().unbind();
+    getInstPort().bind(inst_peer_port);
 
-    if (!getDataPort().isConnected()) {
-        getDataPort().bind(oldCPU->getDataPort().getSlavePort());
-        oldCPU->getDataPort().unBind();
-    }
+    assert(!getDataPort().isConnected());
+    assert(oldCPU->getDataPort().isConnected());
+    SlavePort &data_peer_port = oldCPU->getDataPort().getSlavePort();
+    oldCPU->getDataPort().unbind();
+    getDataPort().bind(data_peer_port);
 }
 
 
diff -r 2cb46eb4ed94 -r e5872950c9a3 src/mem/port.hh
--- a/src/mem/port.hh	Mon Aug 20 15:06:52 2012 +0100
+++ b/src/mem/port.hh	Mon Aug 20 15:34:26 2012 +0100
@@ -140,8 +140,17 @@
                PortID id = InvalidPortID);
     virtual ~MasterPort();
 
-    void unBind();
+    /**
+     * Bind this master port to a slave port. This also does the
+     * mirror action and binds the slave port to the master port.
+     */
     void bind(SlavePort& slave_port);
+
+    /**
+     * Unbind this master port and the associated slave port.
+     */
+    void unbind();
+
     SlavePort& getSlavePort() const;
     bool isConnected() const;
 
@@ -298,8 +307,6 @@
               PortID id = InvalidPortID);
     virtual ~SlavePort();
 
-    void unBind();
-    void bind(MasterPort& master_port);
     MasterPort& getMasterPort() const;
     bool isConnected() const;
 
@@ -387,6 +394,18 @@
   protected:
 
     /**
+     * Called by the master port to unbind. Should never be called
+     * directly.
+     */
+    void unbind();
+
+    /**
+     * Called by the master port to bind. Should never be called
+     * directly.
+     */
+    void bind(MasterPort& master_port);
+
+    /**
      * Receive an atomic request packet from the master port.
      */
     virtual Tick recvAtomic(PacketPtr pkt) = 0;
diff -r 2cb46eb4ed94 -r e5872950c9a3 src/mem/port.cc
--- a/src/mem/port.cc	Mon Aug 20 15:06:52 2012 +0100
+++ b/src/mem/port.cc	Mon Aug 20 15:34:26 2012 +0100
@@ -82,14 +82,22 @@
 }
 
 void
-MasterPort::unBind()
+MasterPort::unbind()
 {
+    if (_slavePort == NULL)
+        panic("Attempting to unbind master port %s that is not connected\n",
+              name());
+    _slavePort->unbind();
     _slavePort = NULL;
 }
 
 void
 MasterPort::bind(SlavePort& slave_port)
 {
+    if (_slavePort != NULL)
+        panic("Attempting to bind master port %s that is already connected\n",
+              name());
+
     // master port keeps track of the slave port
     _slavePort = &slave_port;
 
@@ -173,7 +181,7 @@
 }
 
 void
-SlavePort::unBind()
+SlavePort::unbind()
 {
     _masterPort = NULL;
 }