ruby: Fix block_on behavior

Ruby's controller block_on behavior aimed to block MessageBuffer requests into
SLICC controllers when a Locked_RMW was in flight. Unfortunately, this
functionality only partially works: When non-Locked_RMW memory accesses are
issued to the sequencer to an address with an in-flight Locked_RMW, the
sequencer may pass those accesses through to the controller. At the controller,
a number of incorrect activities can occur depending on the protocol. In
MOESI_hammer, for example, an intermediate IFETCH will cause an L1D to L2
transfer, which cannot be serviced, because the block_on functionality blocks
the trigger queue, resulting in a deadlock. Further, if an intermediate store
arrives (e.g. from a separate SMT thread), the sequencer allows the request
through to the controller, and the atomicity of the Locked_RMW may be broken.

To avoid these problems, disallow the Sequencer from passing any memory
accesses to the controller besides Locked_RMW_Write when a Locked_RMW is in-
flight.

2 files changed, 7 insertions, 0 deletions

diff --git a/src/mem/ruby/slicc_interface/AbstractController.cc b/src/mem/ruby/slicc_interface/AbstractController.cc
index 2a53e53be..5d8b6eeea 100644
--- a/src/mem/ruby/slicc_interface/AbstractController.cc
+++ b/src/mem/ruby/slicc_interface/AbstractController.cc
@@ -192,6 +192,12 @@ AbstractController::blockOnQueue(Addr addr, MessageBuffer* port)
     m_block_map[addr] = port;
 }
 
+bool
+AbstractController::isBlocked(Addr addr) const
+{
+    return m_is_blocking && (m_block_map.find(addr) != m_block_map.end());
+}
+
 void
 AbstractController::unblock(Addr addr)
 {
diff --git a/src/mem/ruby/slicc_interface/AbstractController.hh b/src/mem/ruby/slicc_interface/AbstractController.hh
index cfd11b8eb..6f49e5ec4 100644
--- a/src/mem/ruby/slicc_interface/AbstractController.hh
+++ b/src/mem/ruby/slicc_interface/AbstractController.hh
@@ -73,6 +73,7 @@ class AbstractController : public MemObject, public Consumer
 
     // return instance name
     void blockOnQueue(Addr, MessageBuffer*);
+    bool isBlocked(Addr) const;
     void unblock(Addr);
     bool isBlocked(Addr);