[Qemu-devel] [RFC v2 2/7] exec: Add new exclusive bitmap to ram_list

[Alvise Rigo]

The purpose of this new bitmap is to flag the memory pages that are in
the middle of LL/SC operations (after a LL, before a SC).
For all these pages, the corresponding TLB entries will be generated
in such a way to force the slow-path.
When the system starts, the whole memory is dirty (all the bitmap is
set). A page, after being marked as exclusively-clean, will *not* be
restored as dirty after the SC; the cputlb code will take care of that,
lazily setting the page as dirty when the TLB EXCL entry is about to be
overwritten.

The accessors to this bitmap are currently not atomic, but they have to
be so in a real multi-threading TCG.

Fix also one bracket alignment.

Suggested-by: Jani Kokkonen <address@hidden>
Suggested-by: Claudio Fontana <address@hidden>
Signed-off-by: Alvise Rigo <address@hidden>
---
 exec.c                  |  7 +++++--
 include/exec/memory.h   |  3 ++-
 include/exec/ram_addr.h | 19 +++++++++++++++++++
 3 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/exec.c b/exec.c
index 487583b..79b2571 100644
--- a/exec.c
+++ b/exec.c
@@ -1430,11 +1430,14 @@ static ram_addr_t ram_block_add(RAMBlock *new_block, 
Error **errp)
         int i;
 
         /* ram_list.dirty_memory[] is protected by the iothread lock.  */
-        for (i = 0; i < DIRTY_MEMORY_NUM; i++) {
+        for (i = 0; i < DIRTY_MEMORY_NUM - 1; i++) {
             ram_list.dirty_memory[i] =
                 bitmap_zero_extend(ram_list.dirty_memory[i],
                                    old_ram_size, new_ram_size);
-       }
+        }
+        ram_list.dirty_memory[DIRTY_MEMORY_EXCLUSIVE] =
+                                bitmap_one_extend(ram_list.dirty_memory[i],
+                                old_ram_size, new_ram_size);
     }
     cpu_physical_memory_set_dirty_range(new_block->offset,
                                         new_block->used_length,
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 8ae004e..5ad6f20 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -19,7 +19,8 @@
 #define DIRTY_MEMORY_VGA       0
 #define DIRTY_MEMORY_CODE      1
 #define DIRTY_MEMORY_MIGRATION 2
-#define DIRTY_MEMORY_NUM       3        /* num of dirty bits */
+#define DIRTY_MEMORY_EXCLUSIVE 3
+#define DIRTY_MEMORY_NUM       4        /* num of dirty bits */
 
 #include <stdint.h>
 #include <stdbool.h>
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index c113f21..f097f1b 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -21,6 +21,7 @@
 
 #ifndef CONFIG_USER_ONLY
 #include "hw/xen/xen.h"
+#include "qemu/bitmap.h"
 
 ram_addr_t qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
                                     bool share, const char *mem_path,
@@ -249,5 +250,23 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(unsigned 
long *dest,
     return num_dirty;
 }
 
+/* Exclusive bitmap accessors. */
+static inline void cpu_physical_memory_set_excl_dirty(ram_addr_t addr)
+{
+    set_bit(addr >> TARGET_PAGE_BITS,
+            ram_list.dirty_memory[DIRTY_MEMORY_EXCLUSIVE]);
+}
+
+static inline int cpu_physical_memory_excl_is_dirty(ram_addr_t addr)
+{
+    return test_bit(addr >> TARGET_PAGE_BITS,
+                    ram_list.dirty_memory[DIRTY_MEMORY_EXCLUSIVE]);
+}
+
+static inline void cpu_physical_memory_clear_excl_dirty(ram_addr_t addr)
+{
+    clear_bit(addr >> TARGET_PAGE_BITS,
+              ram_list.dirty_memory[DIRTY_MEMORY_EXCLUSIVE]);
+}
 #endif
 #endif
-- 
2.4.3