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authorAndreas Sandberg <Andreas.Sandberg@ARM.com>2013-01-07 13:05:47 -0500
committerAndreas Sandberg <Andreas.Sandberg@ARM.com>2013-01-07 13:05:47 -0500
commit964aa49d1523787c06491453a85fad511b0a5883 (patch)
treef98a023bc20227f0a06d909df5f42053dd9218f1
parent1814a85a055732baf98fd030441bb4c5c5db9bdc (diff)
downloadgem5-964aa49d1523787c06491453a85fad511b0a5883.tar.xz
mem: Fix guest corruption when caches handle uncacheable accesses
When the classic gem5 cache sees an uncacheable memory access, it used to ignore it or silently drop the cache line in case of a write. Normally, there shouldn't be any data in the cache belonging to an uncacheable address range. However, since some architecture models don't implement cache maintenance instructions, there might be some dirty data in the cache that is discarded when this happens. The reason it has mostly worked before is because such cache lines were most likely evicted by normal memory activity before a TLB flush was requested by the OS. Previously, the cache model would invalidate cache lines when they were accessed by an uncacheable write. This changeset alters this behavior so all uncacheable memory accesses cause a cache flush with an associated writeback if necessary. This is implemented by reusing the cache flushing machinery used when draining the cache, which implies that writebacks are performed using functional accesses.
-rw-r--r--src/mem/cache/cache.hh12
-rw-r--r--src/mem/cache/cache_impl.hh40
2 files changed, 33 insertions, 19 deletions
diff --git a/src/mem/cache/cache.hh b/src/mem/cache/cache.hh
index 5df725683..6b062ef40 100644
--- a/src/mem/cache/cache.hh
+++ b/src/mem/cache/cache.hh
@@ -278,6 +278,18 @@ class Cache : public BaseCache
*/
bool invalidateVisitor(BlkType &blk);
+ /**
+ * Flush a cache line due to an uncacheable memory access to the
+ * line.
+ *
+ * @note This shouldn't normally happen, but we need to handle it
+ * since some architecture models don't implement cache
+ * maintenance operations. We won't even try to get a decent
+ * timing here since the line should have been flushed earlier by
+ * a cache maintenance operation.
+ */
+ void uncacheableFlush(PacketPtr pkt);
+
public:
/** Instantiates a basic cache object. */
Cache(const Params *p, TagStore *tags);
diff --git a/src/mem/cache/cache_impl.hh b/src/mem/cache/cache_impl.hh
index fc01e2c06..a1d945103 100644
--- a/src/mem/cache/cache_impl.hh
+++ b/src/mem/cache/cache_impl.hh
@@ -279,16 +279,7 @@ Cache<TagStore>::access(PacketPtr pkt, BlkType *&blk,
Cycles &lat, PacketList &writebacks)
{
if (pkt->req->isUncacheable()) {
- if (pkt->req->isClearLL()) {
- tags->clearLocks();
- } else if (pkt->isWrite()) {
- blk = tags->findBlock(pkt->getAddr());
- if (blk != NULL) {
- tags->invalidate(blk);
- blk->invalidate();
- }
- }
-
+ uncacheableFlush(pkt);
blk = NULL;
lat = hitLatency;
return false;
@@ -444,15 +435,7 @@ Cache<TagStore>::timingAccess(PacketPtr pkt)
}
if (pkt->req->isUncacheable()) {
- if (pkt->req->isClearLL()) {
- tags->clearLocks();
- } else if (pkt->isWrite()) {
- BlkType *blk = tags->findBlock(pkt->getAddr());
- if (blk != NULL) {
- tags->invalidate(blk);
- blk->invalidate();
- }
- }
+ uncacheableFlush(pkt);
// writes go in write buffer, reads use MSHR
if (pkt->isWrite() && !pkt->isRead()) {
@@ -1104,6 +1087,25 @@ Cache<TagStore>::invalidateVisitor(BlkType &blk)
}
template<class TagStore>
+void
+Cache<TagStore>::uncacheableFlush(PacketPtr pkt)
+{
+ DPRINTF(Cache, "%s%s %x uncacheable\n", pkt->cmdString(),
+ pkt->req->isInstFetch() ? " (ifetch)" : "",
+ pkt->getAddr());
+
+ if (pkt->req->isClearLL())
+ tags->clearLocks();
+
+ BlkType *blk(tags->findBlock(pkt->getAddr()));
+ if (blk) {
+ writebackVisitor(*blk);
+ invalidateVisitor(*blk);
+ }
+}
+
+
+template<class TagStore>
typename Cache<TagStore>::BlkType*
Cache<TagStore>::allocateBlock(Addr addr, PacketList &writebacks)
{