devel/migration/vfio.rst

5 Migration of virtual machine involves saving the state for each device that
13 transferred. The iterative pre-copy phase of migration allows for the guest to
36 for all the devices together.
42 A detailed description of the UAPI for VFIO device migration can be found in
43 the comment for the ``vfio_device_mig_state`` structure in the header file
46 VFIO implements the device hooks for the iterative approach as follows:
54   remaining pre-copy data that the vendor driver has yet to save for the VFIO
59   save for the VFIO device.
79   _STOP_COPY state and iteratively copies the data for the VFIO device until
86   from the VFIO device and queues it for multifd transmission until the vendor
88   After that, it saves the device config space and queues it for multifd
99 * ``cleanup`` functions for both save and load that perform any migration
108 the VFIO device state when certain changes of the migration state occur. For
134 IOMMU support for dirty page tracking. For this reason, all pages are
159 stop-and-copy phase, an IOMMU notifier is used to get a callback for mapped
160 pages and then dirty pages bitmap is fetched from VFIO IOMMU modules for those
167 Below is the state change flow during live migration for a VFIO device that
168 supports both precopy and P2P migration. The flow for devices that don't
169 support it is similar, except that the relevant states for precopy and P2P are
189                 Data of VFIO device for pre-copy phase is copied
198          .save_live_complete_precopy() is called for each active device
199               For the VFIO device: in the non-multifd mode iterate in
216              Incoming migration calls .load_setup() for each device
219      For each device, .load_state() is called for that device section data
221      For data transmitted via multifd channels .load_state_buffer() is called
225   At the end, .load_cleanup() is called for each device and vCPUs are started
234 Postcopy migration is currently not supported for VFIO devices.