On Tue, Jun 25, 2019 at 03:00:24AM +0800, Dr. David Alan Gilbert wrote: > * Kirti Wankhede (kwankh...@nvidia.com) 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? > > That happens at the very end; I think the question here is for something > that gets called at the point we stop iteratively sending RAM, send the > device states and then start sending RAM on demand to the destination > as it's running. Typically we send a small set of device state > (registers etc) at this point. > > I guess there's two different postcopy cases that we need to think > about: > a) Where the VFIO device doesn't support postcopy - it just gets > migrated like any other device, so all it's RAM must get sent > before we flip into postcopy mode. > > b) Where the VFIO device does support postcopy - where the pages > get sent on demand. > > (b) maybe tricky depending on whether your hardware can fault > on pages of your RAM that are needed but not yet transferred; but > if you can that would make life a lot more practical on really > big VFO devices. > > Dave > hi Dave, so do you think it is good to abstract device state data and save it in .pre_save callback?
Thanks Yan > > 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 > > >>> > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
