On 5/9/24 11:09, Avihai Horon wrote:
When migrating a VFIO device that supports pre-copy, it is transitioned
to STOP_COPY twice: once in vfio_vmstate_change() and second time in
vfio_save_complete_precopy().

The second transition is harmless, as it's a STOP_COPY->STOP_COPY no-op
transition. However, with the newly added VFIO migration QAPI event, the
STOP_COPY event is undesirably emitted twice.

Prevent this by returning early in vfio_migration_set_state() if
new_state is the same as current device state.

Note that the STOP_COPY transition in vfio_save_complete_precopy() is
essential for VFIO devices that don't support pre-copy, for migrating an
already stopped guest and for snapshots.

Signed-off-by: Avihai Horon <avih...@nvidia.com>
---
  hw/vfio/migration.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 5a359c4c78..14ef9c924e 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -143,6 +143,10 @@ static int vfio_migration_set_state(VFIODevice *vbasedev,
          (struct vfio_device_feature_mig_state *)feature->data;
      int ret;

I wonder if we should improve the trace events a little to track better
the state transitions. May be move trace_vfio_migration_set_state()
at the beginning of vfio_migration_set_state() and introduce a new
event for the currently named routine set_state() ?

This can come with followups.


Reviewed-by: Cédric Le Goater <c...@redhat.com>

Thanks,

C.


+    if (new_state == migration->device_state) {
+        return 0;
+    }
+
      feature->argsz = sizeof(buf);
      feature->flags =
          VFIO_DEVICE_FEATURE_SET | VFIO_DEVICE_FEATURE_MIG_DEVICE_STATE;


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