1 files changed, 35 insertions, 2 deletions

diff --git a/migration/multifd.c b/migration/multifd.c
index 2541cd2322..9282ab6aa4 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -569,6 +569,7 @@ void multifd_save_cleanup(void)
 int multifd_send_sync_main(QEMUFile *f)
 {
     int i;
+    bool flush_zero_copy;
 
     if (!migrate_use_multifd()) {
         return 0;
@@ -579,6 +580,20 @@ int multifd_send_sync_main(QEMUFile *f)
             return -1;
         }
     }
+
+    /*
+     * When using zero-copy, it's necessary to flush the pages before any of
+     * the pages can be sent again, so we'll make sure the new version of the
+     * pages will always arrive _later_ than the old pages.
+     *
+     * Currently we achieve this by flushing the zero-page requested writes
+     * per ram iteration, but in the future we could potentially optimize it
+     * to be less frequent, e.g. only after we finished one whole scanning of
+     * all the dirty bitmaps.
+     */
+
+    flush_zero_copy = migrate_use_zero_copy_send();
+
     for (i = 0; i < migrate_multifd_channels(); i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
 
@@ -600,6 +615,17 @@ int multifd_send_sync_main(QEMUFile *f)
         ram_counters.transferred += p->packet_len;
         qemu_mutex_unlock(&p->mutex);
         qemu_sem_post(&p->sem);
+
+        if (flush_zero_copy && p->c) {
+            int ret;
+            Error *err = NULL;
+
+            ret = qio_channel_flush(p->c, &err);
+            if (ret < 0) {
+                error_report_err(err);
+                return -1;
+            }
+        }
     }
     for (i = 0; i < migrate_multifd_channels(); i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
@@ -684,8 +710,8 @@ static void *multifd_send_thread(void *opaque)
                 p->iov[0].iov_base = p->packet;
             }
 
-            ret = qio_channel_writev_all(p->c, p->iov, p->iovs_num,
-                                         &local_err);
+            ret = qio_channel_writev_full_all(p->c, p->iov, p->iovs_num, NULL,
+                                              0, p->write_flags, &local_err);
             if (ret != 0) {
                 break;
             }
@@ -913,6 +939,13 @@ int multifd_save_setup(Error **errp)
         /* We need one extra place for the packet header */
         p->iov = g_new0(struct iovec, page_count + 1);
         p->normal = g_new0(ram_addr_t, page_count);
+
+        if (migrate_use_zero_copy_send()) {
+            p->write_flags = QIO_CHANNEL_WRITE_FLAG_ZERO_COPY;
+        } else {
+            p->write_flags = 0;
+        }
+
         socket_send_channel_create(multifd_new_send_channel_async, p);
     }