Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device

[Yan Zhao <yan.y.zhao@intel.com>]

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 state in target vm.

>                         |
>     (FINISH_MIGRATE, _COMPLETED, STOPPED)
>     Migraton thread schedule cleanup bottom half and exit
> 
> Live migration resume path:
>     Incomming migration calls .load_setup for each device
>     (RESTORE_VM, _ACTIVE, STOPPED)
>                         |
>     For each device, .load_state is called for that device section data
>                         |
>     At the end, called .load_cleanup for each device and vCPUs are started.
>                         |
>         (RUNNING, _NONE, _RUNNING)
> 
> Note that:
> - Migration post copy is not supported.
> 
> v3 -> v4:
> - Added one more bit for _RESUMING flag to be set explicitly.
> - data_offset field is read-only for user space application.
> - data_size is read for every iteration before reading data from migration, that
>   is removed assumption that data will be till end of migration region.
> - If vendor driver supports mappable sparsed region, map those region during
>   setup state of save/load, similarly unmap those from cleanup routines.
> - Handles race condition that causes data corruption in migration region during
>   save device state by adding mutex and serialiaing save_buffer and
>   get_dirty_pages routines.
> - Skip called get_dirty_pages routine for mapped MMIO region of device.
> - Added trace events.
> - Splitted into multiple functional patches.
> 
> v2 -> v3:
> - Removed enum of VFIO device states. Defined VFIO device state with 2 bits.
> - Re-structured vfio_device_migration_info to keep it minimal and defined action
>   on read and write access on its members.
> 
> v1 -> v2:
> - Defined MIGRATION region type and sub-type which should be used with region
>   type capability.
> - Re-structured vfio_device_migration_info. This structure will be placed at 0th
>   offset of migration region.
> - Replaced ioctl with read/write for trapped part of migration region.
> - Added both type of access support, trapped or mmapped, for data section of the
>   region.
> - Moved PCI device functions to pci file.
> - Added iteration to get dirty page bitmap until bitmap for all requested pages
>   are copied.
> 
> Thanks,
> Kirti
> 
> 
> Kirti Wankhede (13):
>   vfio: KABI for migration interface
>   vfio: Add function to unmap VFIO region
>   vfio: Add save and load functions for VFIO PCI devices
>   vfio: Add migration region initialization and finalize function
>   vfio: Add VM state change handler to know state of VM
>   vfio: Add migration state change notifier
>   vfio: Register SaveVMHandlers for VFIO device
>   vfio: Add save state functions to SaveVMHandlers
>   vfio: Add load state functions to SaveVMHandlers
>   vfio: Add function to get dirty page list
>   vfio: Add vfio_listerner_log_sync to mark dirty pages
>   vfio: Make vfio-pci device migration capable.
>   vfio: Add trace events in migration code path
> 
>  hw/vfio/Makefile.objs         |   2 +-
>  hw/vfio/common.c              |  55 +++
>  hw/vfio/migration.c           | 815 ++++++++++++++++++++++++++++++++++++++++++
>  hw/vfio/pci.c                 | 126 ++++++-
>  hw/vfio/pci.h                 |  29 ++
>  hw/vfio/trace-events          |  19 +
>  include/hw/vfio/vfio-common.h |  22 ++
>  linux-headers/linux/vfio.h    |  71 ++++
>  8 files changed, 1132 insertions(+), 7 deletions(-)
>  create mode 100644 hw/vfio/migration.c
> 
> -- 
> 2.7.0
>