mem, cpu: Add a separate flag for strictly ordered memory

The Request::UNCACHEABLE flag currently has two different
functions. The first, and obvious, function is to prevent the memory
system from caching data in the request. The second function is to
prevent reordering and speculation in CPU models.

This changeset gives the order/speculation requirement a separate flag
(Request::STRICT_ORDER). This flag prevents CPU models from doing the
following optimizations:

    * Speculation: CPU models are not allowed to issue speculative
      loads.

    * Write combining: CPU models and caches are not allowed to merge
      writes to the same cache line.

Note: The memory system may still reorder accesses unless the
UNCACHEABLE flag is set. It is therefore expected that the
STRICT_ORDER flag is combined with the UNCACHEABLE flag to prevent
this behavior.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/arch/x86/tlb.cc b/src/arch/x86/tlb.cc
index dd0aed770..86e051deb 100644
--- a/src/arch/x86/tlb.cc
+++ b/src/arch/x86/tlb.cc
@@ -206,7 +206,7 @@ TLB::translateInt(RequestPtr req, ThreadContext *tc)
             req->setFlags(Request::MMAPPED_IPR);
             req->setPaddr(MISCREG_PCI_CONFIG_ADDRESS * sizeof(MiscReg));
         } else if ((IOPort & ~mask(2)) == 0xCFC) {
-            req->setFlags(Request::UNCACHEABLE);
+            req->setFlags(Request::UNCACHEABLE | Request::STRICT_ORDER);
             Addr configAddress =
                 tc->readMiscRegNoEffect(MISCREG_PCI_CONFIG_ADDRESS);
             if (bits(configAddress, 31, 31)) {
@@ -217,7 +217,7 @@ TLB::translateInt(RequestPtr req, ThreadContext *tc)
                 req->setPaddr(PhysAddrPrefixIO | IOPort);
             }
         } else {
-            req->setFlags(Request::UNCACHEABLE);
+            req->setFlags(Request::UNCACHEABLE | Request::STRICT_ORDER);
             req->setPaddr(PhysAddrPrefixIO | IOPort);
         }
         return NoFault;
@@ -261,7 +261,7 @@ TLB::finalizePhysical(RequestPtr req, ThreadContext *tc, Mode mode) const
                 return new GeneralProtection(0);
             */
             // Force the access to be uncacheable.
-            req->setFlags(Request::UNCACHEABLE);
+            req->setFlags(Request::UNCACHEABLE | Request::STRICT_ORDER);
             req->setPaddr(x86LocalAPICAddress(tc->contextId(),
                                               paddr - apicRange.start()));
         }
@@ -401,7 +401,7 @@ TLB::translate(RequestPtr req, ThreadContext *tc, Translation *translation,
             DPRINTF(TLB, "Translated %#x -> %#x.\n", vaddr, paddr);
             req->setPaddr(paddr);
             if (entry->uncacheable)
-                req->setFlags(Request::UNCACHEABLE);
+                req->setFlags(Request::UNCACHEABLE | Request::STRICT_ORDER);
         } else {
             //Use the address which already has segmentation applied.
             DPRINTF(TLB, "Paging disabled.\n");