[Qemu-devel] [PATCH 21/22] memory: make cpu_physical_memory_sync_dirty_bitmap() fully atomic

[Paolo Bonzini]

From: Stefan Hajnoczi <address@hidden>

The fast path of cpu_physical_memory_sync_dirty_bitmap() directly
manipulates the dirty bitmap.  Use atomic_xchg() to make the
test-and-clear atomic.

Signed-off-by: Stefan Hajnoczi <address@hidden>
Message-Id: <address@hidden>
[Only do xchg on nonzero words. - Paolo]
Signed-off-by: Paolo Bonzini <address@hidden>
---
 include/exec/ram_addr.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index b7357ac..c4e5624 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -220,12 +220,12 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(unsigned 
long *dest,
 
         for (k = page; k < page + nr; k++) {
             if (src[k]) {
+                unsigned long bits = atomic_xchg(&src[k], 0);
                 unsigned long new_dirty;
                 new_dirty = ~dest[k];
-                dest[k] |= src[k];
-                new_dirty &= src[k];
+                dest[k] |= bits;
+                new_dirty &= bits;
                 num_dirty += ctpopl(new_dirty);
-                src[k] = 0;
             }
         }
     } else {
-- 
2.3.3