From: Paolo Bonzini <pbonzini@redhat.com>
Date: Wed, 12 Aug 2015 07:41:40 +0000 (+0200)
Subject: tcg: add memory barriers in page_find_alloc accesses
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=6940fab84b826175cf90d48d0e3da1b76518f5b4;p=qemu.git

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 37bb56ca42..5329982518 100644
--- 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));