tcg: add memory barriers in page_find_alloc accesses

page_find is reading the radix tree outside all locks, so it has to
use the RCU primitives.  It does not need RCU critical sections
because the PageDescs are never removed, so there is never a need
to wait for the end of code sections that use a PageDesc.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/translate-all.c b/translate-all.c
index 37bb56ca42f2242201a6a5dd68eb8a60a8c8410a..532998251821d03a16f2181a0c50c24bb3934d0d 100644 (file)
--- a/translate-all.c
+++ b/translate-all.c
@@ -431,26 +431,26 @@ static PageDesc *page_find_alloc(tb_page_addr_t index, int alloc)
 
     /* Level 2..N-1.  */
     for (i = V_L1_SHIFT / V_L2_BITS - 1; i > 0; i--) {
-        void **p = *lp;
+        void **p = atomic_rcu_read(lp);
 
         if (p == NULL) {
             if (!alloc) {
                 return NULL;
             }
             p = g_new0(void *, V_L2_SIZE);
-            *lp = p;
+            atomic_rcu_set(lp, p);
         }
 
         lp = p + ((index >> (i * V_L2_BITS)) & (V_L2_SIZE - 1));
     }
 
-    pd = *lp;
+    pd = atomic_rcu_read(lp);
     if (pd == NULL) {
         if (!alloc) {
             return NULL;
         }
         pd = g_new0(PageDesc, V_L2_SIZE);
-        *lp = pd;
+        atomic_rcu_set(lp, pd);
     }
 
     return pd + (index & (V_L2_SIZE - 1));