We now issue host memory barriers to match the guest memory order.
Continue to disable MTTCG only if the guest has not been ported.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 accel/tcg/tcg-all.c | 39 ++++++++++-----------------------------
 1 file changed, 10 insertions(+), 29 deletions(-)

diff --git a/accel/tcg/tcg-all.c b/accel/tcg/tcg-all.c
index 02af6a2891..03dfd67e9e 100644
--- a/accel/tcg/tcg-all.c
+++ b/accel/tcg/tcg-all.c
@@ -64,37 +64,23 @@ DECLARE_INSTANCE_CHECKER(TCGState, TCG_STATE,
  * they can set the appropriate CONFIG flags in ${target}-softmmu.mak
  *
  * Once a guest architecture has been converted to the new primitives
- * there are two remaining limitations to check.
- *
- * - The guest can't be oversized (e.g. 64 bit guest on 32 bit host)
- * - The host must have a stronger memory order than the guest
- *
- * It may be possible in future to support strong guests on weak hosts
- * but that will require tagging all load/stores in a guest with their
- * implicit memory order requirements which would likely slow things
- * down a lot.
+ * there is one remaining limitation to check:
+ *   - The guest can't be oversized (e.g. 64 bit guest on 32 bit host)
  */
 
-static bool check_tcg_memory_orders_compatible(void)
-{
-#if defined(TCG_GUEST_DEFAULT_MO) && defined(TCG_TARGET_DEFAULT_MO)
-    return (TCG_GUEST_DEFAULT_MO & ~TCG_TARGET_DEFAULT_MO) == 0;
-#else
-    return false;
-#endif
-}
-
 static bool default_mttcg_enabled(void)
 {
     if (icount_enabled() || TCG_OVERSIZED_GUEST) {
         return false;
-    } else {
-#ifdef TARGET_SUPPORTS_MTTCG
-        return check_tcg_memory_orders_compatible();
-#else
-        return false;
-#endif
     }
+#ifdef TARGET_SUPPORTS_MTTCG
+# ifndef TCG_GUEST_DEFAULT_MO
+#  error "TARGET_SUPPORTS_MTTCG without TCG_GUEST_DEFAULT_MO"
+# endif
+    return true;
+#else
+    return false;
+#endif
 }
 
 static void tcg_accel_instance_init(Object *obj)
@@ -162,11 +148,6 @@ static void tcg_set_thread(Object *obj, const char *value, Error **errp)
             warn_report("Guest not yet converted to MTTCG - "
                         "you may get unexpected results");
 #endif
-            if (!check_tcg_memory_orders_compatible()) {
-                warn_report("Guest expects a stronger memory ordering "
-                            "than the host provides");
-                error_printf("This may cause strange/hard to debug errors\n");
-            }
             s->mttcg_enabled = true;
         }
     } else if (strcmp(value, "single") == 0) {
-- 
2.34.1