O3: Fixes fetch deadlock when the interrupt clears before CPU handles it.

When this condition occurs the cpu should restart the fetch stage to fetch from
the original execution path. Fault handling in the commit stage is cleaned up a
little bit so the control flow is simplier. Finally, if an instruction is being
used to carry a fault it isn't executed, so the fault propagates appropriately.

1 files changed, 58 insertions, 44 deletions

diff --git a/src/cpu/o3/commit_impl.hh b/src/cpu/o3/commit_impl.hh
index 2912cbb03..7f37b5f09 100644
--- a/src/cpu/o3/commit_impl.hh
+++ b/src/cpu/o3/commit_impl.hh
@@ -674,54 +674,67 @@ template <class Impl>
 void
 DefaultCommit<Impl>::handleInterrupt()
 {
-    if (interrupt != NoFault) {
-        // Wait until the ROB is empty and all stores have drained in
-        // order to enter the interrupt.
-        if (rob->isEmpty() && !iewStage->hasStoresToWB()) {
-            // Squash or record that I need to squash this cycle if
-            // an interrupt needed to be handled.
-            DPRINTF(Commit, "Interrupt detected.\n");
+    // Verify that we still have an interrupt to handle
+    if (!cpu->checkInterrupts(cpu->tcBase(0))) {
+        DPRINTF(Commit, "Pending interrupt is cleared by master before "
+                "it got handled. Restart fetching from the orig path.\n");
+        toIEW->commitInfo[0].clearInterrupt = true;
+        interrupt = NoFault;
+        return;
+    }
 
-            // Clear the interrupt now that it's going to be handled
-            toIEW->commitInfo[0].clearInterrupt = true;
+    // Wait until the ROB is empty and all stores have drained in
+    // order to enter the interrupt.
+    if (rob->isEmpty() && !iewStage->hasStoresToWB()) {
+        // Squash or record that I need to squash this cycle if
+        // an interrupt needed to be handled.
+        DPRINTF(Commit, "Interrupt detected.\n");
 
-            assert(!thread[0]->inSyscall);
-            thread[0]->inSyscall = true;
+        // Clear the interrupt now that it's going to be handled
+        toIEW->commitInfo[0].clearInterrupt = true;
 
-            // CPU will handle interrupt.
-            cpu->processInterrupts(interrupt);
+        assert(!thread[0]->inSyscall);
+        thread[0]->inSyscall = true;
 
-            thread[0]->inSyscall = false;
+        // CPU will handle interrupt.
+        cpu->processInterrupts(interrupt);
 
-            commitStatus[0] = TrapPending;
+        thread[0]->inSyscall = false;
 
-            // Generate trap squash event.
-            generateTrapEvent(0);
+        commitStatus[0] = TrapPending;
 
-            interrupt = NoFault;
-        } else {
-            DPRINTF(Commit, "Interrupt pending, waiting for ROB to empty.\n");
-        }
-    } else if (commitStatus[0] != TrapPending &&
-               cpu->checkInterrupts(cpu->tcBase(0)) &&
-               !trapSquash[0] &&
-               !tcSquash[0]) {
-        // Process interrupts if interrupts are enabled, not in PAL
-        // mode, and no other traps or external squashes are currently
-        // pending.
-        // @todo: Allow other threads to handle interrupts.
-
-        // Get any interrupt that happened
-        interrupt = cpu->getInterrupts();
-
-        if (interrupt != NoFault) {
-            // Tell fetch that there is an interrupt pending.  This
-            // will make fetch wait until it sees a non PAL-mode PC,
-            // at which point it stops fetching instructions.
-            toIEW->commitInfo[0].interruptPending = true;
-        }
+        // Generate trap squash event.
+        generateTrapEvent(0);
+
+        interrupt = NoFault;
+    } else {
+        DPRINTF(Commit, "Interrupt pending, waiting for ROB to empty.\n");
     }
 }
+
+template <class Impl>
+void
+DefaultCommit<Impl>::propagateInterrupt()
+{
+    if (commitStatus[0] == TrapPending || interrupt || trapSquash[0] ||
+            tcSquash[0])
+        return;
+
+    // Process interrupts if interrupts are enabled, not in PAL
+    // mode, and no other traps or external squashes are currently
+    // pending.
+    // @todo: Allow other threads to handle interrupts.
+
+    // Get any interrupt that happened
+    interrupt = cpu->getInterrupts();
+
+    // Tell fetch that there is an interrupt pending.  This
+    // will make fetch wait until it sees a non PAL-mode PC,
+    // at which point it stops fetching instructions.
+    if (interrupt != NoFault)
+        toIEW->commitInfo[0].interruptPending = true;
+}
+
 #endif // FULL_SYSTEM
 
 template <class Impl>
@@ -730,12 +743,13 @@ DefaultCommit<Impl>::commit()
 {
 
 #if FULL_SYSTEM
-    // Check for any interrupt, and start processing it.  Or if we
-    // have an outstanding interrupt and are at a point when it is
-    // valid to take an interrupt, process it.
-    if (cpu->checkInterrupts(cpu->tcBase(0))) {
+    // Check for any interrupt that we've already squashed for and start processing it.
+    if (interrupt != NoFault)
         handleInterrupt();
-    }
+
+    // Check if we have a interrupt and get read to handle it
+    if (cpu->checkInterrupts(cpu->tcBase(0)))
+        propagateInterrupt();
 #endif // FULL_SYSTEM
 
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