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[Qemu-devel] [PATCH v8 00/13] Add migration support for VFIO device

From: Kirti Wankhede
Subject: [Qemu-devel] [PATCH v8 00/13] Add migration support for VFIO device
Date: Tue, 27 Aug 2019 00:25:40 +0530

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
- 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:

Live migration save path:
        QEMU normal running state
    migrate_init spawns migration_thread.
    Migration thread then calls each device's .save_setup()
    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.
    For VFIO device, iterate in  .save_live_complete_precopy  until
    pending data is 0.
    Migraton thread schedule cleanup bottom half and exit

Live migration resume path:
    Incomming migration calls .load_setup for each device
    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.

Note that:
- Migration post copy is not supported.

v7 -> v8:
- Updated comments for KABI
- Added BAR address validation check during PCI device's config space load as
  suggested by Dr. David Alan Gilbert.
- Changed vfio_migration_set_state() to set or clear device state flags.
- Some nit fixes.

v6 -> v7:
- Fix build failures.

v5 -> v6:
- Fix build failure.

v4 -> v5:
- Added decriptive comment about the sequence of access of members of structure
  vfio_device_migration_info to be followed based on Alex's suggestion
- Updated get dirty pages sequence.
- As per Cornelia Huck's suggestion, added callbacks to VFIODeviceOps to
  get_object, save_config and load_config.
- Fixed multiple nit picks.
- Tested live migration with multiple vfio device assigned to a VM.

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
- Moved PCI device functions to pci file.
- Added iteration to get dirty page bitmap until bitmap for all requested pages
  are copied.


Kirti Wankhede (13):
  vfio: KABI for migration interface
  vfio: Add function to unmap VFIO region
  vfio: Add vfio_get_object callback to VFIODeviceOps
  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_listener_log_sync to mark dirty pages
  vfio: Make vfio-pci device migration capable.

 hw/vfio/Makefile.objs         |   2 +-
 hw/vfio/common.c              |  55 +++
 hw/vfio/migration.c           | 848 ++++++++++++++++++++++++++++++++++++++++++
 hw/vfio/pci.c                 | 191 +++++++++-
 hw/vfio/trace-events          |  19 +
 include/hw/vfio/vfio-common.h |  22 ++
 linux-headers/linux/vfio.h    | 148 ++++++++
 7 files changed, 1278 insertions(+), 7 deletions(-)
 create mode 100644 hw/vfio/migration.c


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