On Fri, Jun 21, 2019 at 05:22:37PM +0800, Kirti Wankhede wrote: > > > On 6/21/2019 2:16 PM, Yan Zhao wrote: > > On Fri, Jun 21, 2019 at 04:02:50PM +0800, Kirti Wankhede wrote: > >> > >> > >> On 6/21/2019 6:54 AM, Yan Zhao wrote: > >>> On Fri, Jun 21, 2019 at 08:25:18AM +0800, Yan Zhao wrote: > >>>> On Thu, Jun 20, 2019 at 10:37:28PM +0800, Kirti Wankhede wrote: > >>>>> Add migration support for VFIO device > >>>>> > >>>>> This Patch set include patches as below: > >>>>> - Define KABI for VFIO device for migration support. > >>>>> - Added save and restore functions for PCI configuration space > >>>>> - Generic migration functionality for VFIO device. > >>>>> * This patch set adds functionality only for PCI devices, but can be > >>>>> extended to other VFIO devices. > >>>>> * Added all the basic functions required for pre-copy, stop-and-copy > >>>>> and > >>>>> resume phases of migration. > >>>>> * Added state change notifier and from that notifier function, VFIO > >>>>> device's state changed is conveyed to VFIO device driver. > >>>>> * During save setup phase and resume/load setup phase, migration > >>>>> region > >>>>> is queried and is used to read/write VFIO device data. > >>>>> * .save_live_pending and .save_live_iterate are implemented to use > >>>>> QEMU's > >>>>> functionality of iteration during pre-copy phase. > >>>>> * In .save_live_complete_precopy, that is in stop-and-copy phase, > >>>>> iteration to read data from VFIO device driver is implemented till > >>>>> pending > >>>>> bytes returned by driver are not zero. > >>>>> * Added function to get dirty pages bitmap for the pages which are > >>>>> used by > >>>>> driver. > >>>>> - Add vfio_listerner_log_sync to mark dirty pages. > >>>>> - Make VFIO PCI device migration capable. If migration region is not > >>>>> provided by > >>>>> driver, migration is blocked. > >>>>> > >>>>> Below is the flow of state change for live migration where states in > >>>>> brackets > >>>>> represent VM state, migration state and VFIO device state as: > >>>>> (VM state, MIGRATION_STATUS, VFIO_DEVICE_STATE) > >>>>> > >>>>> Live migration save path: > >>>>> QEMU normal running state > >>>>> (RUNNING, _NONE, _RUNNING) > >>>>> | > >>>>> migrate_init spawns migration_thread. > >>>>> (RUNNING, _SETUP, _RUNNING|_SAVING) > >>>>> Migration thread then calls each device's .save_setup() > >>>>> | > >>>>> (RUNNING, _ACTIVE, _RUNNING|_SAVING) > >>>>> If device is active, get pending bytes by .save_live_pending() > >>>>> if pending bytes >= threshold_size, call save_live_iterate() > >>>>> Data of VFIO device for pre-copy phase is copied. > >>>>> Iterate till pending bytes converge and are less than threshold > >>>>> | > >>>>> On migration completion, vCPUs stops and calls > >>>>> .save_live_complete_precopy > >>>>> for each active device. VFIO device is then transitioned in > >>>>> _SAVING state. > >>>>> (FINISH_MIGRATE, _DEVICE, _SAVING) > >>>>> For VFIO device, iterate in .save_live_complete_precopy until > >>>>> pending data is 0. > >>>>> (FINISH_MIGRATE, _DEVICE, _STOPPED) > >>>> > >>>> I suggest we also register to VMStateDescription, whose .pre_save > >>>> handler would get called after .save_live_complete_precopy in pre-copy > >>>> only case, and will called before .save_live_iterate in post-copy > >>>> enabled case. > >>>> In the .pre_save handler, we can save all device state which must be > >>>> copied after device stop in source vm and before device start in target > >>>> vm. > >>>> > >>> hi > >>> to better describe this idea: > >>> > >>> in pre-copy only case, the flow is > >>> > >>> start migration --> .save_live_iterate (several round) -> stop source vm > >>> --> .save_live_complete_precopy --> .pre_save -->start target vm > >>> -->migration complete > >>> > >>> > >>> in post-copy enabled case, the flow is > >>> > >>> start migration --> .save_live_iterate (several round) --> start post > >>> copy --> > >>> stop source vm --> .pre_save --> start target vm --> .save_live_iterate > >>> (several round) > >>> -->migration complete > >>> > >>> Therefore, we should put saving of device state in .pre_save interface > >>> rather than in .save_live_complete_precopy. > >>> The device state includes pci config data, page tables, register state, > >>> etc. > >>> > >>> The .save_live_iterate and .save_live_complete_precopy should only deal > >>> with saving dirty memory. > >>> > >> > >> Vendor driver can decide when to save device state depending on the VFIO > >> device state set by user. Vendor driver doesn't have to depend on which > >> callback function QEMU or user application calls. In pre-copy case, > >> save_live_complete_precopy sets VFIO device state to > >> VFIO_DEVICE_STATE_SAVING which means vCPUs are stopped and vendor driver > >> should save all device state. > >> > > when post copy stops vCPUs and vfio device, vendor driver only needs to > > provide device state. but how vendor driver knows that, if no extra > > interface or no extra device state is provides? > > > > .save_live_complete_postcopy interface for post-copy will get called, > right? > yes, but it's too late after postcopy completion
> Thanks, > Kirti > > >>> > >>> I know current implementation does not support post-copy. but at least > >>> it should not require huge change when we decide to enable it in future. > >>> > >> > >> .has_postcopy and .save_live_complete_postcopy need to be implemented to > >> support post-copy. I think .save_live_complete_postcopy should be > >> similar to vfio_save_complete_precopy. > >> > >> Thanks, > >> Kirti > >> > >>> Thanks > >>> Yan > >>>
