[Qemu-devel] [RFC 3/6] memory: use atomic ops for setting dirty memory bits

[Stefan Hajnoczi <stefanha@redhat.com>]

Use set_bit_atomic() and bitmap_set_atomic() so that multiple threads
can dirty memory without race conditions.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
I had to get creative to stay under 80 characters per line.  I'm open to
suggestions if you prefer me to format it another way.
---
 include/exec/ram_addr.h | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index 8fc75cd..ba90daa 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -93,30 +93,32 @@ static inline void cpu_physical_memory_set_dirty_flag(ram_addr_t addr,
                                                       unsigned client)
 {
     assert(client < DIRTY_MEMORY_NUM);
-    set_bit(addr >> TARGET_PAGE_BITS, ram_list.dirty_memory[client]);
+    set_bit_atomic(addr >> TARGET_PAGE_BITS, ram_list.dirty_memory[client]);
 }
 
 static inline void cpu_physical_memory_set_dirty_range_nocode(ram_addr_t start,
                                                               ram_addr_t length)
 {
     unsigned long end, page;
+    unsigned long **dirty_memory = ram_list.dirty_memory;
 
     end = TARGET_PAGE_ALIGN(start + length) >> TARGET_PAGE_BITS;
     page = start >> TARGET_PAGE_BITS;
-    bitmap_set(ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION], page, end - page);
-    bitmap_set(ram_list.dirty_memory[DIRTY_MEMORY_VGA], page, end - page);
+    bitmap_set_atomic(dirty_memory[DIRTY_MEMORY_MIGRATION], page, end - page);
+    bitmap_set_atomic(dirty_memory[DIRTY_MEMORY_VGA], page, end - page);
 }
 
 static inline void cpu_physical_memory_set_dirty_range(ram_addr_t start,
                                                        ram_addr_t length)
 {
     unsigned long end, page;
+    unsigned long **dirty_memory = ram_list.dirty_memory;
 
     end = TARGET_PAGE_ALIGN(start + length) >> TARGET_PAGE_BITS;
     page = start >> TARGET_PAGE_BITS;
-    bitmap_set(ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION], page, end - page);
-    bitmap_set(ram_list.dirty_memory[DIRTY_MEMORY_VGA], page, end - page);
-    bitmap_set(ram_list.dirty_memory[DIRTY_MEMORY_CODE], page, end - page);
+    bitmap_set_atomic(dirty_memory[DIRTY_MEMORY_MIGRATION], page, end - page);
+    bitmap_set_atomic(dirty_memory[DIRTY_MEMORY_VGA], page, end - page);
+    bitmap_set_atomic(dirty_memory[DIRTY_MEMORY_CODE], page, end - page);
     xen_modified_memory(start, length);
 }
 
@@ -142,10 +144,11 @@ static inline void cpu_physical_memory_set_dirty_lebitmap(unsigned long *bitmap,
         for (k = 0; k < nr; k++) {
             if (bitmap[k]) {
                 unsigned long temp = leul_to_cpu(bitmap[k]);
+                unsigned long **d = ram_list.dirty_memory;
 
-                ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION][page + k] |= temp;
-                ram_list.dirty_memory[DIRTY_MEMORY_VGA][page + k] |= temp;
-                ram_list.dirty_memory[DIRTY_MEMORY_CODE][page + k] |= temp;
+                atomic_or(&d[DIRTY_MEMORY_MIGRATION][page + k], temp);
+                atomic_or(&d[DIRTY_MEMORY_VGA][page + k], temp);
+                atomic_or(&d[DIRTY_MEMORY_CODE][page + k], temp);
             }
         }
         xen_modified_memory(start, pages);
-- 
2.1.0