[Qemu-devel] [PATCH 08/10] tcg: add memory barriers in page_find_alloc accesses

[Paolo Bonzini]

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 <pbonz...@redhat.com>
---
 translate-all.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/translate-all.c b/translate-all.c
index 7727091..78a787d 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -437,14 +437,14 @@ 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));
@@ -456,7 +456,7 @@ static PageDesc *page_find_alloc(tb_page_addr_t index, int 
alloc)
             return NULL;
         }
         pd = g_new0(PageDesc, V_L2_SIZE);
-        *lp = pd;
+        atomic_rcu_set(lp, pd);
     }
 
     return pd + (index & (V_L2_SIZE - 1));
-- 
1.8.3.1