From 22b60c57e697289baa205f11b164f356363c2bee Mon Sep 17 00:00:00 2001
From: Gedare Bloom <gedare@rtems.org>
Date: Tue, 21 May 2013 11:40:11 -0500
Subject: [PATCH] x86: Squash outstanding walks when instructions are squashed.
 This is the x86 version of the ARM changeset baa17ba80e06. In case an
 instruction has been squashed by the o3 cpu, this patch allows page table
 walker to avoid carrying out a pending translation that the instruction
 requested for.

---
 src/arch/x86/X86TLB.py           |  2 ++
 src/arch/x86/pagetable_walker.cc | 37 +++++++++++++++++++++++++++-----
 src/arch/x86/pagetable_walker.hh | 10 ++++++++-
 3 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/src/arch/x86/X86TLB.py b/src/arch/x86/X86TLB.py
index a08dbb138..b652118ce 100644
--- a/src/arch/x86/X86TLB.py
+++ b/src/arch/x86/X86TLB.py
@@ -47,6 +47,8 @@ class X86PagetableWalker(MemObject):
     cxx_header = 'arch/x86/pagetable_walker.hh'
     port = MasterPort("Port for the hardware table walker")
     system = Param.System(Parent.any, "system object")
+    num_squash_per_cycle = Param.Unsigned(4,
+            "Number of outstanding walks that can be squashed per cycle")
 
 class X86TLB(BaseTLB):
     type = 'X86TLB'
diff --git a/src/arch/x86/pagetable_walker.cc b/src/arch/x86/pagetable_walker.cc
index 853e062e7..45f902999 100644
--- a/src/arch/x86/pagetable_walker.cc
+++ b/src/arch/x86/pagetable_walker.cc
@@ -139,11 +139,8 @@ Walker::recvTimingResp(PacketPtr pkt)
         delete senderWalk;
         // Since we block requests when another is outstanding, we
         // need to check if there is a waiting request to be serviced
-        if (currStates.size()) {
-            WalkerState * newState = currStates.front();
-            if (!newState->wasStarted())
-                newState->startWalk();
-        }
+        if (currStates.size())
+            startWalkWrapper();
     }
     return true;
 }
@@ -192,6 +189,36 @@ Walker::WalkerState::initState(ThreadContext * _tc,
     timing = _isTiming;
 }
 
+void
+Walker::startWalkWrapper()
+{
+    unsigned num_squashed = 0;
+    WalkerState *currState = currStates.front();
+    while ((num_squashed < numSquashable) && currState &&
+        currState->translation->squashed()) {
+        currStates.pop_front();
+        num_squashed++;
+
+        DPRINTF(PageTableWalker, "Squashing table walk for address %#x\n",
+            currState->req->getVaddr());
+
+        // finish the translation which will delete the translation object
+        currState->translation->finish(new UnimpFault("Squashed Inst"),
+                currState->req, currState->tc, currState->mode);
+
+        // delete the current request
+        delete currState;
+
+        // check the next translation request, if it exists
+        if (currStates.size())
+            currState = currStates.front();
+        else
+            currState = NULL;
+    }
+    if (currState && !currState->wasStarted())
+        currState->startWalk();
+}
+
 Fault
 Walker::WalkerState::startWalk()
 {
diff --git a/src/arch/x86/pagetable_walker.hh b/src/arch/x86/pagetable_walker.hh
index c2781ca1b..c6766689b 100644
--- a/src/arch/x86/pagetable_walker.hh
+++ b/src/arch/x86/pagetable_walker.hh
@@ -87,6 +87,7 @@ namespace X86ISA
         // State to track each walk of the page table
         class WalkerState
         {
+          friend class Walker;
           private:
             enum State {
                 Ready,
@@ -176,6 +177,12 @@ namespace X86ISA
         System * sys;
         MasterID masterId;
 
+        // The number of outstanding walks that can be squashed per cycle.
+        unsigned numSquashable;
+
+        // Wrapper for checking for squashes before starting a translation.
+        void startWalkWrapper();
+
         // Functions for dealing with packets.
         bool recvTimingResp(PacketPtr pkt);
         void recvRetry();
@@ -199,7 +206,8 @@ namespace X86ISA
         Walker(const Params *params) :
             MemObject(params), port(name() + ".port", this),
             funcState(this, NULL, NULL, true), tlb(NULL), sys(params->system),
-            masterId(sys->getMasterId(name()))
+            masterId(sys->getMasterId(name())),
+            numSquashable(params->num_squash_per_cycle)
         {
         }
     };
-- 
2.30.2