[Qemu-devel] [PATCH] migration: always initial RAMBlock.bmap to 1 for new migration

[Ivan Ren <renyime@gmail.com>]

Reproduce the problem:
migrate
migrate_cancel
migrate

Error happen for memory migration

The reason as follows:
1. qemu start, ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] all set to
   1 by a series of cpu_physical_memory_set_dirty_range
2. migration start:ram_init_bitmaps
   - memory_global_dirty_log_start: begin log diry
   - memory_global_dirty_log_sync: sync dirty bitmap to
     ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION]
   - migration_bitmap_sync_range: sync ram_list.
     dirty_memory[DIRTY_MEMORY_MIGRATION] to RAMBlock.bmap
     and ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] is set to zero
3. migration data...
4. migrate_cancel, will stop log dirty
5. migration start:ram_init_bitmaps
   - memory_global_dirty_log_start: begin log diry
   - memory_global_dirty_log_sync: sync dirty bitmap to
     ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION]
   - migration_bitmap_sync_range: sync ram_list.
     dirty_memory[DIRTY_MEMORY_MIGRATION] to RAMBlock.bmap
     and ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] is set to zero

   Here RAMBlock.bmap only have new logged dirty pages, don't contain
   the whole guest pages.

Signed-off-by: Ivan Ren <ivanren@tencent.com>
---
 migration/ram.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index 908517fc2b..bbebaee0c1 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -3173,11 +3173,11 @@ static int ram_state_init(RAMState **rsp)
     QSIMPLEQ_INIT(&(*rsp)->src_page_requests);
 
     /*
+     * Count the total number of pages used by ram blocks not including any
+     * gaps due to alignment or unplugs.
      * This must match with the initial values of dirty bitmap.
-     * Currently we initialize the dirty bitmap to all zeros so
-     * here the total dirty page count is zero.
      */
-    (*rsp)->migration_dirty_pages = 0;
+    (*rsp)->migration_dirty_pages = ram_bytes_total() >> TARGET_PAGE_BITS;
     ram_state_reset(*rsp);
 
     return 0;
@@ -3196,12 +3196,13 @@ static void ram_list_init_bitmaps(void)
              * The initial dirty bitmap for migration must be set with all
              * ones to make sure we'll migrate every guest RAM page to
              * destination.
-             * Here we didn't set RAMBlock.bmap simply because it is already
-             * set in ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] in
-             * ram_block_add, and that's where we'll sync the dirty bitmaps.
-             * Here setting RAMBlock.bmap would be fine too but not necessary.
+             * Here we set RAMBlock.bmap all to 1 because when rebegin a
+             * new migration after a failed migration, ram_list.
+             * dirty_memory[DIRTY_MEMORY_MIGRATION] don't include the whole
+             * guest memory.
              */
             block->bmap = bitmap_new(pages);
+            bitmap_set(block->bmap, 0, pages);
             if (migrate_postcopy_ram()) {
                 block->unsentmap = bitmap_new(pages);
                 bitmap_set(block->unsentmap, 0, pages);
-- 
2.17.2 (Apple Git-113)