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>
5fcadd7d14