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According to VFIO uAPI, precopy initial_bytes is considered as critical data that should be transferred and loaded prior to moving to STOP_COPY state to ensure precopy phase would be effective. As currently defined, initial_bytes can only decrease as it's being read from the data fd. However, there are cases where a new chunk of initial_bytes should be transferred during precopy. The new VFIO_PRECOPY_INFO_REINIT feature addresses this and allows reporting a new value for initial_bytes regardless of any previously reported values. Implement VFIO_PRECOPY_INFO_REINIT feature: 1. Opt-in for VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2 to make VFIO_PRECOPY_INFO_REINIT available. 2. Request a new switchover ACK if initial_bytes increases post of a previous switchover ACK. This ensures the device is not moved to STOP_COPY before initial_bytes has reached zero again. Acked-by: Peter Xu <peterx@redhat.com> Signed-off-by: Avihai Horon <avihaih@nvidia.com> Link: https://lore.kernel.org/qemu-devel/20260706085211.13905-13-avihaih@nvidia.com Signed-off-by: Cédric Le Goater <clg@redhat.com>