ARM: Squash outstanding walks when instructions are squashed.

src/arch/arm/ArmTLB.py

@@ -47,6 +47,8 @@ class ArmTableWalker(MemObject):
     cxx_class = 'ArmISA::TableWalker'
     port = MasterPort("Port for TableWalker to do walk the translation with")
     sys = Param.System(Parent.any, "system object parameter")
+    num_squash_per_cycle = Param.Unsigned(2,
+            "Number of outstanding walks that can be squashed per cycle")
 
 class ArmTLB(SimObject):
     type = 'ArmTLB'

src/arch/arm/table_walker.cc

@@ -54,6 +54,7 @@ TableWalker::TableWalker(const Params *p)
     : MemObject(p), port(this, params()->sys), drainEvent(NULL),
       tlb(NULL), currState(NULL), pending(false),
       masterId(p->sys->getMasterId(name())),
+      numSquashable(p->num_squash_per_cycle),
       doL1DescEvent(this), doL2DescEvent(this), doProcessEvent(this)
 {
     sctlr = 0;
@@ -184,9 +185,46 @@ TableWalker::processWalkWrapper()
     assert(!currState);
     assert(pendingQueue.size());
     currState = pendingQueue.front();
-    pendingQueue.pop_front();
+
-    pending = true;
+
-    processWalk();
+    if (!currState->transState->squashed()) {
+        // We've got a valid request, lets process it
+        pending = true;
+        pendingQueue.pop_front();
+        processWalk();
+        return;
+    }
+
+
+    // If the instruction that we were translating for has been
+    // squashed we shouldn't bother.
+    unsigned num_squashed = 0;
+    ThreadContext *tc = currState->tc;
+    assert(currState->transState->squashed());
+    while ((num_squashed < numSquashable) && currState &&
+            currState->transState->squashed()) {
+        pendingQueue.pop_front();
+        num_squashed++;
+
+        DPRINTF(TLB, "Squashing table walk for address %#x\n", currState->vaddr);
+
+        // finish the translation which will delete the translation object
+        currState->transState->finish(new UnimpFault("Squashed Inst"),
+                currState->req, currState->tc, currState->mode);
+
+        // delete the current request
+        delete currState;
+
+        // peak at the next one
+        if (pendingQueue.size())
+            currState = pendingQueue.front();
+        else
+            currState = NULL;
+    }
+
+    // if we've still got pending translations schedule more work
+    nextWalk(tc);
+    currState = NULL;
 }
 
 Fault

src/arch/arm/table_walker.hh

@@ -380,6 +380,10 @@ class TableWalker : public MemObject
     /** Request id for requests generated by this walker */
     MasterID masterId;
 
+    /** The number of walks belonging to squashed instructions that can be
+     * removed from the pendingQueue per cycle. */
+    unsigned numSquashable;
+
   public:
     typedef ArmTableWalkerParams Params;
     TableWalker(const Params *p);

src/cpu/simple/timing.hh

@@ -269,6 +269,14 @@ class TimingSimpleCPU : public BaseSimpleCPU
     void completeDataAccess(PacketPtr pkt);
     void advanceInst(Fault fault);
 
+    /** This function is used by the page table walker to determine if it could
+     * translate the a pending request or if the underlying request has been
+     * squashed. This always returns false for the simple timing CPU as it never
+     * executes any instructions speculatively.
+     * @ return Is the current instruction squashed?
+     */
+    bool isSquashed() const { return false; }
+
     /**
      * Print state of address in memory system via PrintReq (for
      * debugging).

src/cpu/translation.hh

@@ -259,6 +259,12 @@ class DataTranslation : public BaseTLB::Translation
         }
         delete this;
     }
+
+    bool
+    squashed() const
+    {
+        return xc->isSquashed();
+    }
 };
 
 #endif // __CPU_TRANSLATION_HH__

src/sim/tlb.hh

@@ -94,6 +94,13 @@ class BaseTLB : public SimObject
          */
         virtual void finish(Fault fault, RequestPtr req, ThreadContext *tc,
                             Mode mode) = 0;
+
+        /** This function is used by the page table walker to determine if it
+         * should translate the a pending request or if the underlying request
+         * has been squashed.
+         * @ return Is the instruction that requested this translation squashed?
+         */
+        virtual bool squashed() const { return false; }
     };
 };