diff -r fbc330c4dd8b -r cabe32e23f17 src/mem/cache/cache.cc
--- a/src/mem/cache/cache.cc	Tue Dec 29 16:36:53 2015 +0000
+++ b/src/mem/cache/cache.cc	Tue Dec 29 16:43:30 2015 +0000
@@ -185,7 +185,11 @@
         if (pkt->isLLSC()) {
             blk->trackLoadLocked(pkt);
         }
+
+        // all read responses have a data payload
+        assert(pkt->hasRespData());
         pkt->setDataFromBlock(blk->data, blkSize);
+
         // determine if this read is from a (coherent) cache, or not
         // by looking at the command type; we could potentially add a
         // packet attribute such as 'FromCache' to make this check a
@@ -796,10 +800,7 @@
             }
 
             pkt->makeTimingResponse();
-            // for debugging, set all the bits in the response data
-            // (also keeps valgrind from complaining when debugging settings
-            //  print out instruction results)
-            std::memset(pkt->getPtr<uint8_t>(), 0xFF, pkt->getSize());
+
             // request_time is used here, taking into account lat and the delay
             // charged if the packet comes from the xbar.
             cpuSidePort->schedTimingResp(pkt, request_time, true);
@@ -2039,7 +2040,10 @@
             doTimingSupplyResponse(pkt, blk->data, is_deferred, pending_inval);
         } else {
             pkt->makeAtomicResponse();
-            pkt->setDataFromBlock(blk->data, blkSize);
+            // packets such as upgrades do not actually have any data
+            // payload
+            if (pkt->hasData())
+                pkt->setDataFromBlock(blk->data, blkSize);
         }
     }
 
diff -r fbc330c4dd8b -r cabe32e23f17 src/mem/cache/mshr.cc
--- a/src/mem/cache/mshr.cc	Tue Dec 29 16:36:53 2015 +0000
+++ b/src/mem/cache/mshr.cc	Tue Dec 29 16:43:30 2015 +0000
@@ -115,16 +115,26 @@
 static void
 replaceUpgrade(PacketPtr pkt)
 {
+    // remember if the current packet has data allocated
+    bool has_data = pkt->hasData() || pkt->hasRespData();
     if (pkt->cmd == MemCmd::UpgradeReq) {
         pkt->cmd = MemCmd::ReadExReq;
         DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
     } else if (pkt->cmd == MemCmd::SCUpgradeReq) {
         pkt->cmd = MemCmd::SCUpgradeFailReq;
+        // same as above, we need to allocate space
         DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
     } else if (pkt->cmd == MemCmd::StoreCondReq) {
         pkt->cmd = MemCmd::StoreCondFailReq;
         DPRINTF(Cache, "Replacing StoreCondReq with StoreCondFailReq\n");
     }
+
+    if (!has_data && (pkt->hasData() || pkt->hasRespData())) {
+        // we went from a packet that had no data (neither request,
+        // nor response), to one that does, and therefore we need to
+        // actually allocate space for the data payload
+        pkt->allocate();
+    }
 }
 
 
diff -r fbc330c4dd8b -r cabe32e23f17 src/mem/packet.hh
--- a/src/mem/packet.hh	Tue Dec 29 16:36:53 2015 +0000
+++ b/src/mem/packet.hh	Tue Dec 29 16:43:30 2015 +0000
@@ -521,6 +521,11 @@
     bool isEviction() const          { return cmd.isEviction(); }
     bool isWriteback() const         { return cmd.isWriteback(); }
     bool hasData() const             { return cmd.hasData(); }
+    bool hasRespData() const
+    {
+        MemCmd resp_cmd = cmd.responseCommand();
+        return resp_cmd.hasData();
+    }
     bool isLLSC() const              { return cmd.isLLSC(); }
     bool isError() const             { return cmd.isError(); }
     bool isPrint() const             { return cmd.isPrint(); }
@@ -1071,9 +1076,13 @@
     void
     allocate()
     {
-        assert(flags.noneSet(STATIC_DATA|DYNAMIC_DATA));
-        flags.set(DYNAMIC_DATA);
-        data = new uint8_t[getSize()];
+        // if either this command or the response command has a data
+        // payload, actually allocate space
+        if (hasData() || hasRespData()) {
+            assert(flags.noneSet(STATIC_DATA|DYNAMIC_DATA));
+            flags.set(DYNAMIC_DATA);
+            data = new uint8_t[getSize()];
+        }
     }
 
     /** @} */