Re: [PATCH] vfio/migration: Skip log_sync during migration SETUP state

[Cédric Le Goater]

On 4/3/23 15:00, Avihai Horon wrote:
> Currently, VFIO log_sync can be issued while migration is in SETUP
> state. However, doing this log_sync is at best redundant and at worst
> can fail.
>
> Redundant -- all RAM is marked dirty in migration SETUP state and is
> transferred only after migration is set to ACTIVE state, so doing
> log_sync during migration SETUP is pointless.
>
> Can fail -- there is a time window, between setting migration state to
> SETUP and starting dirty tracking by RAM save_live_setup handler, during
> which dirty tracking is still not started. Any VFIO log_sync call that
> is issued during this time window will fail. For example, this error can
> be triggered by migrating a VM when a GUI is active, which constantly
> calls log_sync.
>
> Fix it by skipping VFIO log_sync while migration is in SETUP state.
>
> Fixes: 758b96b61d5c ("vfio/migrate: Move switch of dirty tracking into 
> vfio_memory_listener")
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
migration is still experimental, so this can wait 8.1. Correct me if not.

Thanks,

C.

> ---
>   hw/vfio/common.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 4d01ea3515..78358ede27 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -478,7 +478,8 @@ static bool vfio_devices_all_dirty_tracking(VFIOContainer 
> *container)
>       VFIODevice *vbasedev;
>       MigrationState *ms = migrate_get_current();
>   
> -    if (!migration_is_setup_or_active(ms->state)) {
> +    if (ms->state != MIGRATION_STATUS_ACTIVE &&
> +        ms->state != MIGRATION_STATUS_DEVICE) {
>           return false;
>       }
>