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mem: Do not alter cache block state on uncacheable snoops

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This patch ensures we do not respond with a Modified (dirty and
writable) line if the request is uncacheable, and that the cache
responding retains the line without modifying the state (even if
responding).
This commit is contained in:
Andreas Hansson 2015-12-31 09:33:25 -05:00
parent 0fcb376e5f
commit f1ec326be5
1 changed files with 24 additions and 7 deletions
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31
src/mem/cache/cache.cc vendored
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@ -1904,6 +1904,13 @@ Cache::handleSnoop(PacketPtr pkt, CacheBlk *blk, bool is_timing,
bool invalidate = pkt->isInvalidate();
bool M5_VAR_USED needs_writable = pkt->needsWritable();
// at the moment we could get an uncacheable write which does not
// have the invalidate flag, and we need a suitable way of dealing
// with this case
panic_if(invalidate && pkt->req->isUncacheable(),
"%s got an invalidating uncacheable snoop request %s to %#llx",
name(), pkt->cmdString(), pkt->getAddr());
uint32_t snoop_delay = 0;
if (forwardSnoops) {
@ -1988,15 +1995,18 @@ Cache::handleSnoop(PacketPtr pkt, CacheBlk *blk, bool is_timing,
return snoop_delay;
}
if (!pkt->req->isUncacheable() && pkt->isRead() && !invalidate) {
// reading without requiring the line in a writable state,
// note that we retain the block as Owned if it is Modified
// (dirty data), with the response taken care of below, and
// otherwhise simply downgrade from Exclusive to Shared (or
// remain in Shared)
if (pkt->isRead() && !invalidate) {
// reading without requiring the line in a writable state
assert(!needs_writable);
pkt->setHasSharers();
blk->status &= ~BlkWritable;
// if the requesting packet is uncacheable, retain the line in
// the current state, otherwhise unset the writable flag,
// which means we go from Modified to Owned (and will respond
// below), remain in Owned (and will respond below), from
// Exclusive to Shared, or remain in Shared
if (!pkt->req->isUncacheable())
blk->status &= ~BlkWritable;
}
if (respond) {
@ -2020,6 +2030,13 @@ Cache::handleSnoop(PacketPtr pkt, CacheBlk *blk, bool is_timing,
// we already called setHasSharers above
}
// if we are returning a writable and dirty (Modified) line,
// we should be invalidating the line
panic_if(!invalidate && !pkt->hasSharers(),
"%s is passing a Modified line through %s to %#llx, "
"but keeping the block",
name(), pkt->cmdString(), pkt->getAddr());
if (is_timing) {
doTimingSupplyResponse(pkt, blk->data, is_deferred, pending_inval);
} else {