o3: Fix issue with LLSC ordering and speculation

This patch unlocks the cpu-local monitor when the CPU sees a snoop to a locked
address. Previously we relied on the cache to handle the locking for us, however
some users on the gem5 mailing list reported a case where the cpu speculatively
executes a ll operation after a pending sc operation in the pipeline and that
makes the cache monitor valid. This should handle that case by invaliding the
local monitor.

1 files changed, 29 insertions, 0 deletions

diff --git a/src/arch/mips/locked_mem.hh b/src/arch/mips/locked_mem.hh
index 60df8252a..b4003fea9 100644
--- a/src/arch/mips/locked_mem.hh
+++ b/src/arch/mips/locked_mem.hh
@@ -1,4 +1,16 @@
 /*
+ * Copyright (c) 2012 ARM Limited
+ * All rights reserved
+ *
+ * The license below extends only to copyright in the software and shall
+ * not be construed as granting a license to any other intellectual
+ * property including but not limited to intellectual property relating
+ * to a hardware implementation of the functionality of the software
+ * licensed hereunder.  You may use the software subject to the license
+ * terms below provided that you ensure that this notice is replicated
+ * unmodified and in its entirety in all distributions of the software,
+ * modified or unmodified, in source code or in binary form.
+ *
  * Copyright (c) 2006-2007 The Regents of The University of Michigan
  * All rights reserved.
  *
@@ -41,10 +53,27 @@
 #include "base/misc.hh"
 #include "base/trace.hh"
 #include "debug/LLSC.hh"
+#include "mem/packet.hh"
 #include "mem/request.hh"
 
 namespace MipsISA
 {
+template <class XC>
+inline void
+handleLockedSnoop(XC *xc, PacketPtr pkt, Addr cacheBlockMask)
+{
+    if (!xc->readMiscReg(MISCREG_LLFLAG))
+        return;
+
+    Addr locked_addr = xc->readMiscReg(MISCREG_LLADDR) & cacheBlockMask;
+    Addr snoop_addr = pkt->getAddr();
+
+    assert((cacheBlockMask & snoop_addr) == snoop_addr);
+
+    if (locked_addr == snoop_addr)
+        xc->setMiscReg(MISCREG_LLFLAG, false);
+}
+
 
 template <class XC>
 inline void