memory: replace cpu_physical_memory_reset_dirty() with test-and-clear

The cpu_physical_memory_reset_dirty() function is sometimes used
together with cpu_physical_memory_get_dirty().  This is not atomic since
two separate accesses to the dirty memory bitmap are made.

Turn cpu_physical_memory_reset_dirty() and
cpu_physical_memory_clear_dirty_range_type() into the atomic
cpu_physical_memory_test_and_clear_dirty().

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <1417519399-3166-6-git-send-email-stefanha@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 17 insertions, 6 deletions

diff --git a/exec.c b/exec.c
index 162c57908e..487583b1bd 100644
--- a/exec.c
+++ b/exec.c
@@ -852,16 +852,27 @@ static void tlb_reset_dirty_range_all(ram_addr_t start, ram_addr_t length)
 }
 
 /* Note: start and end must be within the same ram block.  */
-void cpu_physical_memory_reset_dirty(ram_addr_t start, ram_addr_t length,
-                                     unsigned client)
+bool cpu_physical_memory_test_and_clear_dirty(ram_addr_t start,
+                                              ram_addr_t length,
+                                              unsigned client)
 {
-    if (length == 0)
-        return;
-    cpu_physical_memory_clear_dirty_range_type(start, length, client);
+    unsigned long end, page;
+    bool dirty;
 
-    if (tcg_enabled()) {
+    if (length == 0) {
+        return false;
+    }
+
+    end = TARGET_PAGE_ALIGN(start + length) >> TARGET_PAGE_BITS;
+    page = start >> TARGET_PAGE_BITS;
+    dirty = bitmap_test_and_clear_atomic(ram_list.dirty_memory[client],
+                                         page, end - page);
+
+    if (dirty && tcg_enabled()) {
         tlb_reset_dirty_range_all(start, length);
     }
+
+    return dirty;
 }
 
 /* Called from RCU critical section */