migration/ram: Use migration_bitmap_sync_precopy() for postcopy discard

ram_postcopy_send_discard_bitmap() performs the final RAM dirty bitmap
sync at postcopy switchover, before sending discard bitmap to the
destination. Unlike the precopy switchover path, it currently calls the
raw migration_bitmap_sync() helper and passes last_stage=false.

Postcopy switchover is also a stopped-VM final sync point, so use
migration_bitmap_sync_precopy(true). This keeps RAM final bitmap sync
handling consistent across precopy and postcopy switchover, including
the precopy bitmap-sync notifier wrapper. Current notifier users are
safe in postcopy: virtio-balloon free-page hinting already opts out when
postcopy-ram is enabled [1].

This prepares for moving the final sync out of RAM completion/discard
paths and into migration_switchover_start(), where the migration core
can run a final save_query_pending pass for all modules uniformly.

[1] fd51e54fa102 ("virtio-balloon: don't start free page hinting if postcopy is possible")

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Link: https://lore.kernel.org/qemu-devel/20260706085211.13905-3-avihaih@nvidia.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

diff --git a/migration/ram.c b/migration/ram.c
index bd519f1931cb0d0cde27765a95730179aba03027..55aa9b47dc8ab8463fd1aeba19726a493b81b070 100644 (file)
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2687,7 +2687,7 @@ void ram_postcopy_send_discard_bitmap(MigrationState *ms)
     RCU_READ_LOCK_GUARD();
 
     /* This should be our last sync, the src is now paused */
-    migration_bitmap_sync(rs, false);
+    migration_bitmap_sync_precopy(true);
 
     /* Easiest way to make sure we don't resume in the middle of a host-page */
     rs->pss[RAM_CHANNEL_PRECOPY].last_sent_block = NULL;