+
+* A ``load_state`` function that loads the config section and the data
+ sections that are generated by the save functions above
+
+* ``cleanup`` functions for both save and load that perform any migration
+ related cleanup, including unmapping the migration region
+
+A VM state change handler is registered to change the VFIO device state when
+the VM state changes.
+
+Similarly, a migration state change notifier is registered to get a
+notification on migration state change. These states are translated to the
+corresponding VFIO device state and conveyed to the vendor driver.
+
+System memory dirty pages tracking
+----------------------------------
+
+A ``log_sync`` memory listener callback marks those system memory pages
+as dirty which are used for DMA by the VFIO device. The dirty pages bitmap is
+queried per container. All pages pinned by the vendor driver through external
+APIs have to be marked as dirty during migration. When there are CPU writes,
+CPU dirty page tracking can identify dirtied pages, but any page pinned by the
+vendor driver can also be written by device. There is currently no device or
+IOMMU support for dirty page tracking in hardware.
+
+By default, dirty pages are tracked when the device is in pre-copy as well as
+stop-and-copy phase. So, a page pinned by vendor driver will be copied to
+destination in both the phases. Copying dirty pages in pre-copy phase helps
+QEMU to predict if it can achieve its downtime tolerances. If QEMU during
+pre-copy phase keeps finding dirty pages continuously, then it understands
+that even in stop-and-copy phase, it is likely to find dirty pages and can
+predict the downtime accordingly
+
+QEMU also provides per device opt-out option ``pre-copy-dirty-page-tracking``
+which disables querying dirty bitmap during pre-copy phase. If it is set to
+off, all dirty pages will be copied to destination in stop-and-copy phase only
+
+System memory dirty pages tracking when vIOMMU is enabled
+---------------------------------------------------------
+
+With vIOMMU, an IO virtual address range can get unmapped while in pre-copy
+phase of migration. In that case, the unmap ioctl returns any dirty pages in
+that range and QEMU reports corresponding guest physical pages dirty. During
+stop-and-copy phase, an IOMMU notifier is used to get a callback for mapped
+pages and then dirty pages bitmap is fetched from VFIO IOMMU modules for those
+mapped ranges.
+
+Flow of state changes during Live migration
+===========================================
+
+Below is the flow of state change during live migration.
+The values in the brackets represent the VM state, the migration state, and
+the VFIO device state, respectively.
+
+Live migration save path
+------------------------
+
+::
+
+ QEMU normal running state
+ (RUNNING, _NONE, _RUNNING)
+ |
+ migrate_init spawns migration_thread
+ Migration thread then calls each device's .save_setup()
+ (RUNNING, _SETUP, _RUNNING|_SAVING)
+ |
+ (RUNNING, _ACTIVE, _RUNNING|_SAVING)
+ If device is active, get pending_bytes by .save_live_pending()
+ If total pending_bytes >= threshold_size, call .save_live_iterate()
+ Data of VFIO device for pre-copy phase is copied
+ Iterate till total pending bytes converge and are less than threshold
+ |
+ On migration completion, vCPU stops and calls .save_live_complete_precopy for
+ each active device. The VFIO device is then transitioned into _SAVING state
+ (FINISH_MIGRATE, _DEVICE, _SAVING)
+ |
+ For the VFIO device, iterate in .save_live_complete_precopy until
+ pending data is 0
+ (FINISH_MIGRATE, _DEVICE, _STOPPED)
+ |
+ (FINISH_MIGRATE, _COMPLETED, _STOPPED)
+ Migraton thread schedules cleanup bottom half and exits
+
+Live migration resume path
+--------------------------
+
+::
+
+ Incoming migration calls .load_setup for each device
+ (RESTORE_VM, _ACTIVE, _STOPPED)
+ |
+ For each device, .load_state is called for that device section data
+ (RESTORE_VM, _ACTIVE, _RESUMING)
+ |
+ At the end, .load_cleanup is called for each device and vCPUs are started
+ (RUNNING, _NONE, _RUNNING)
+
+Postcopy
+========
+
+Postcopy migration is currently not supported for VFIO devices.
