On Fri, Jun 28, 2019 at 05:44:47PM +0800, Dr. David Alan Gilbert wrote: > * Yan Zhao (yan.y.z...@intel.com) wrote: > > 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? > > I'm not sure we have a vmsd/pre_save in this setup? If we did then it's > a bit confusing because I don't think we have any other iterative device > that also has a vmsd. Yes, I tried it. it's ok to register SaveVMHandlers and VMStateDescription at the same time.
> > I'd have to test it, but I think you might get the devices > ->save_live_complete_precopy called at the right point just before > postcopy switchover. It's worth looking. > if a iterative device supports postcopy, then its save_live_complete_precopy would not get called before postcopy switchover. However, postcopy may need to save pure device state only data (not memory) at that time. That's the reason I think we should also register to VMStateDescription also, as its .pre_save handler would get called at at that time. Thanks Yan > Dave > > > 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 > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK