@@ -4419,6 +4419,42 @@ static int ram_resume_prepare(MigrationState *s, void *opaque)
return 0;
}
+static bool ram_save_postcopy_prepare(QEMUFile *f, void *opaque, Error **errp)
+{
+ int ret;
+
+ if (migrate_multifd()) {
+ /*
+ * When multifd is enabled, source QEMU needs to make sure all the
+ * pages queued before postcopy starts to be flushed.
+ *
+ * Meanwhile, the load of these pages must happen before switching
+ * to postcopy. It's because loading of guest pages (so far) in
+ * multifd recv threads is still non-atomic, so the load cannot
+ * happen with vCPUs running on destination side.
+ *
+ * This flush and sync will guarantee those pages loaded _before_
+ * postcopy starts on destination. The rational is, this happens
+ * before VM stops (and before source QEMU sends all the rest of
+ * the postcopy messages). So when the destination QEMU received
+ * the postcopy messages, it must have received the sync message on
+ * the main channel (either RAM_SAVE_FLAG_MULTIFD_FLUSH, or
+ * RAM_SAVE_FLAG_EOS), and such message should have guaranteed all
+ * previous guest pages queued in the multifd channels to be
+ * completely loaded.
+ */
+ ret = multifd_ram_flush_and_sync(f);
+ if (ret < 0) {
+ error_setg(errp, "%s: multifd flush and sync failed", __func__);
+ return false;
+ }
+ }
+
+ qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
+
+ return true;
+}
+
void postcopy_preempt_shutdown_file(MigrationState *s)
{
qemu_put_be64(s->postcopy_qemufile_src, RAM_SAVE_FLAG_EOS);
@@ -4438,6 +4474,7 @@ static SaveVMHandlers savevm_ram_handlers = {
.load_setup = ram_load_setup,
.load_cleanup = ram_load_cleanup,
.resume_prepare = ram_resume_prepare,
+ .save_postcopy_prepare = ram_save_postcopy_prepare,
};
static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,