[PATCH v1 06/13] migrate/ram: Discard new RAM when growing RAM blocks and the VM is stopped

[David Hildenbrand <david@redhat.com>]

In case we grow our RAM after ram_postcopy_incoming_init() (e.g., when
synchronizing the RAM block state with the migration source), the resized
part would not get discarded. Let's perform that when being notified
about a resize while postcopy has been advised and the guest is not
running yet.

Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 migration/ram.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/migration/ram.c b/migration/ram.c
index 57f32011a3..cbd54947fb 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -3722,6 +3722,25 @@ static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,
         return;
     }
 
+    /*
+     * Especially at the start of precopy on the migration target, before
+     * starting postcopy, we synchronize the RAM block sizes. Let's make sure
+     * that any resizes before starting the guest are properly handled by
+     * postcopy. Note: All other postcopy handling (e.g., registering handlers,
+     * disabling THP) happens after all resizes (e.g., during precopy) were
+     * performed.
+     */
+    if (postcopy_is_advised() && !runstate_is_running()) {
+        /* Update what ram_postcopy_incoming_init()->init_range() does. */
+        if (old_size < new_size) {
+            if (ram_discard_range(rb->idstr, old_size, new_size - old_size)) {
+                error_report("RAM block '%s' discard of resized RAM failed",
+                             rb->idstr);
+            }
+        }
+        return;
+    }
+
     /*
      * Some resizes are triggered on the migration target by precopy code,
      * when synchronizing RAM block sizes. In these cases, the VM is not
-- 
2.24.1