Re: [PATCH 3/3] vfio/migration: Don't emit STOP_COPY state change event twice

["Cédric Le Goater" <clg@redhat.com>]

Hello Avihai,

On 4/30/24 07:16, 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 migration state change QAPI
> event, the STOP_COPY state change event is undesirably emitted twice.
> 
> Prevent this by conditionally transitioning to STOP_COPY state in
> vfio_save_complete_precopy().
> 
> 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 <avihaih@nvidia.com>
> ---
>   hw/vfio/migration.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 6bbccf6545..30a2b2ea74 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -591,14 +591,17 @@ static int vfio_save_iterate(QEMUFile *f, void *opaque)
>   static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
>   {
>       VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
>       ssize_t data_size;
>       int ret;
>   
>       /* We reach here with device state STOP or STOP_COPY only */
> -    ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP_COPY,
> -                                   VFIO_DEVICE_STATE_STOP);
> -    if (ret) {
> -        return ret;
> +    if (migration->device_state == VFIO_DEVICE_STATE_STOP) {

Shouldn't we handle no-op transitions in vfio_migration_set_state()
instead ?

Thanks,

C.



> +        ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP_COPY,
> +                                       VFIO_DEVICE_STATE_STOP);
> +        if (ret) {
> +            return ret;
> +        }
>       }
>   
>       do {