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authorMrinmoy Ghosh <mrinmoy.ghosh@arm.com>2013-02-15 17:40:10 -0500
committerMrinmoy Ghosh <mrinmoy.ghosh@arm.com>2013-02-15 17:40:10 -0500
commit8cef39fb6742d834e383f533539ba90f72bbc7d9 (patch)
treeb390315c48692bcb3fce65bfda3fb747600b93bb /src/arch/arm
parent3af59ab386ba297b99d2a215f4c5efa10d0cfe56 (diff)
downloadgem5-8cef39fb6742d834e383f533539ba90f72bbc7d9.tar.xz
arm: fix a page table walker issue where a page could be translated multiple times
If multiple memory operations to the same page are miss the TLB they are all inserted into the page table queue and before this change could result in multiple uncessesary walks as well as duplicate enteries being inserted into the TLB.
Diffstat (limited to 'src/arch/arm')
-rw-r--r--src/arch/arm/table_walker.cc33
-rw-r--r--src/arch/arm/tlb.cc2
-rw-r--r--src/arch/arm/tlb.hh16
3 files changed, 33 insertions, 18 deletions
diff --git a/src/arch/arm/table_walker.cc b/src/arch/arm/table_walker.cc
index 44f12833b..9755299ff 100644
--- a/src/arch/arm/table_walker.cc
+++ b/src/arch/arm/table_walker.cc
@@ -186,8 +186,15 @@ TableWalker::processWalkWrapper()
assert(pendingQueue.size());
currState = pendingQueue.front();
-
- if (!currState->transState->squashed()) {
+ // Check if a previous walk filled this request already
+ TlbEntry* te = tlb->lookup(currState->vaddr, currState->contextId, true);
+
+ // Check if we still need to have a walk for this request. If the requesting
+ // instruction has been squashed, or a previous walk has filled the TLB with
+ // a match, we just want to get rid of the walk. The latter could happen
+ // when there are multiple outstanding misses to a single page and a
+ // previous request has been successfully translated.
+ if (!currState->transState->squashed() && !te) {
// We've got a valid request, lets process it
pending = true;
pendingQueue.pop_front();
@@ -200,26 +207,34 @@ TableWalker::processWalkWrapper()
// 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()) {
+ (currState->transState->squashed() || te)) {
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);
+ if (currState->transState->squashed()) {
+ // finish the translation which will delete the translation object
+ currState->transState->finish(new UnimpFault("Squashed Inst"),
+ currState->req, currState->tc, currState->mode);
+ } else {
+ // translate the request now that we know it will work
+ currState->fault = tlb->translateTiming(currState->req, currState->tc,
+ currState->transState, currState->mode);
+ }
// delete the current request
delete currState;
// peak at the next one
- if (pendingQueue.size())
+ if (pendingQueue.size()) {
currState = pendingQueue.front();
- else
+ te = tlb->lookup(currState->vaddr, currState->contextId, true);
+ } else {
+ // Terminate the loop, nothing more to do
currState = NULL;
+ }
}
// if we've still got pending translations schedule more work
diff --git a/src/arch/arm/tlb.cc b/src/arch/arm/tlb.cc
index 170d819d8..6b864b980 100644
--- a/src/arch/arm/tlb.cc
+++ b/src/arch/arm/tlb.cc
@@ -107,7 +107,7 @@ TLB::lookup(Addr va, uint8_t cid, bool functional)
if (table[x].match(va, cid)) {
// We only move the hit entry ahead when the position is higher than rangeMRU
- if (x > rangeMRU) {
+ if (x > rangeMRU && !functional) {
TlbEntry tmp_entry = table[x];
for(int i = x; i > 0; i--)
table[i] = table[i-1];
diff --git a/src/arch/arm/tlb.hh b/src/arch/arm/tlb.hh
index f5c7320ed..c1eba1ba7 100644
--- a/src/arch/arm/tlb.hh
+++ b/src/arch/arm/tlb.hh
@@ -91,14 +91,6 @@ class TLB : public BaseTLB
TableWalker *tableWalker;
- /** Lookup an entry in the TLB
- * @param vpn virtual address
- * @param asn context id/address space id to use
- * @param functional if the lookup should modify state
- * @return pointer to TLB entrry if it exists
- */
- TlbEntry *lookup(Addr vpn, uint8_t asn, bool functional = false);
-
// Access Stats
mutable Stats::Scalar instHits;
mutable Stats::Scalar instMisses;
@@ -132,6 +124,14 @@ class TLB : public BaseTLB
typedef ArmTLBParams Params;
TLB(const Params *p);
+ /** Lookup an entry in the TLB
+ * @param vpn virtual address
+ * @param asn context id/address space id to use
+ * @param functional if the lookup should modify state
+ * @return pointer to TLB entrry if it exists
+ */
+ TlbEntry *lookup(Addr vpn, uint8_t asn, bool functional = false);
+
virtual ~TLB();
int getsize() const { return size; }