Re: [PATCH 09/14] vfio/migration: Re-query precopy size before sending VFIO_MIG_FLAG_DEV_INIT_DATA_SENT

[Avihai Horon]

On 5/7/2026 11:24 AM, Cédric Le Goater wrote:

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Hello Avihai

On 5/5/26 10:14, Avihai Horon wrote:

When precopy initial_bytes reaches zero VFIO_MIG_FLAG_DEV_INIT_DATA_SENT
flag is sent to the destination to indicate that initial data has been
sent, so destination can indicate back to source when it finished
loading it.

To get a more accurate estimation of initial_bytes, re-query precopy
size before sending the flag. Extract the flag sending logic from
vfio_save_iterate() to a new helper for clarity.

I would prefer to separate the changes, so a patch for this new routine,
and then :

This may prevent premature sending of VFIO_MIG_FLAG_DEV_INIT_DATA_SENT
flag if, for example, the previously queried initial_bytes was lower
than actually is. Additionally, it prevents sending the flag if
vfio_query_precopy_size() failed.

Of course, will do.

Thanks.

Signed-off-by: Avihai Horon <avih...@nvidia.com>
---
  hw/vfio/migration.c  | 37 ++++++++++++++++++++++++++++++++-----
  hw/vfio/trace-events |  1 +
  2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 2911583ee1..243624b5fe 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c

@@ -456,6 +456,37 @@ static void vfio_update_estimated_pending_data(VFIOMigration *migration,

                                           data_size);
  }

+/* Returns true if the init data flag was sent, false otherwise */

+static bool vfio_send_init_data_flag(QEMUFile *f, VFIOMigration *migration)

+{
+    VFIODevice *vbasedev = migration->vbasedev;
+    int ret;
+
+    if (!migrate_switchover_ack()) {
+        return false;
+    }
+
+    if (migration->precopy_init_size || migration->initial_data_sent) {
+        return false;
+    }
+
+    /*

+     * precopy_init_size holds an estimation of the initial data size, re-query +     * precopy size to ensure it's really zero before sending init data flag.

+     * Don't send the flag if query fails.
+     */
+    ret = vfio_query_precopy_size(migration);
+    if (ret || migration->precopy_init_size) {
+        return false;
+    }
+
+    qemu_put_be64(f, VFIO_MIG_FLAG_DEV_INIT_DATA_SENT);
+    migration->initial_data_sent = true;
+    trace_vfio_send_init_data_flag(vbasedev->name);
+
+    return true;
+}
+
  static bool vfio_precopy_supported(VFIODevice *vbasedev)
  {
      VFIOMigration *migration = vbasedev->migration;

@@ -664,11 +695,7 @@ static int vfio_save_iterate(QEMUFile *f, void *opaque)

      vfio_update_estimated_pending_data(migration, data_size);

-    if (migrate_switchover_ack() && !migration->precopy_init_size &&
-        !migration->initial_data_sent) {
-        qemu_put_be64(f, VFIO_MIG_FLAG_DEV_INIT_DATA_SENT);
-        migration->initial_data_sent = true;
-    } else {
+    if (!vfio_send_init_data_flag(f, migration)) {
          qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
      }

diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
index ab27ff5ea2..e91858354c 100644
--- a/hw/vfio/trace-events
+++ b/hw/vfio/trace-events

@@ -176,6 +176,7 @@ vfio_save_iterate(const char *name, uint64_t precopy_init_size, uint64_t precopy

  vfio_save_iterate_start(const char *name) " (%s)"

  vfio_save_setup(const char *name, uint64_t data_buffer_size) " (%s) data buffer size %"PRIu64   vfio_state_pending(const char *name, uint64_t stopcopy_size, uint64_t precopy_init_size, uint64_t precopy_dirty_size, bool exact) " (%s) stopcopy size %"PRIu64" precopy initial size %"PRIu64" precopy dirty size %"PRIu64 " exact %d"

+vfio_send_init_data_flag(const char *name) " (%s)"

  vfio_vmstate_change(const char *name, int running, const char *reason, const char *dev_state) " (%s) running %d reason %s device state %s"   vfio_vmstate_change_prepare(const char *name, int running, const char *reason, const char *dev_state) " (%s) running %d reason %s device state %s"