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[PATCH v9 Qemu 00/15] Add migration support for VFIO devices
[PATCH v9 Qemu 00/15] Add migration support for VFIO devices
Tue, 12 Nov 2019 22:35:09 +0530
This Patch set adds migration support for VFIO devices in QEMU.
This Patch set include patches as below:
- Define KABI for VFIO device for migration support for device state and newly
added ioctl definations to get dirty pages bitmap. These 3 patches are same as
the first 2 patches in kernel patch set.
- Few code refactor
- 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.
- Add vfio_listerner_log_sync to mark dirty pages. Dirty pages bitmap is queried
per container. All pages pinned by vendor driver through vfio_pin_pages
external API has to be marked as dirty during migration.
When there are CPU writes, CPU dirty page tracking can identify dirtied
pages, but any page pinned by vendor driver can also be written by
device. As of now there is no device which has hardware support for
dirty page tracking. So all pages which are pinned by vendor driver
should be considered as dirty.
In Qemu, marking pages dirty is only done when device is in stop-and-copy
phase because if pages are marked dirty during pre-copy phase and content is
transfered from source to distination, there is no way to know newly dirtied
pages from the point they were copied earlier until device stops. To avoid
repeated copy of same content, pinned pages are marked dirty only during
- With vIOMMU, IO virtual address range can get unmapped while in pre-copy
phase of migration. In that case, unmap ioctl should return pages pinned
in that range and QEMU should report corresponding guest physical pages
- Make VFIO PCI device migration capable. If migration region is not provided by
driver, migration is blocked.
Since there is no device which has hardware support for system memmory
dirty bitmap tracking, right now there is no other API from vendor driver
to VFIO IOMMU module to report dirty pages. In future, when such hardware
support will be implemented, an API will be required in kernel such that
vendor driver could report dirty pages to VFIO module during migration phases.
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
(FINISH_MIGRATE, _DEVICE, _SAVING)
For VFIO device, iterate in .save_live_complete_precopy until
pending data is 0.
(FINISH_MIGRATE, _DEVICE, _STOPPED)
(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)
- Migration post copy is not supported.
v8 -> v9:
- Split patch set in 2 sets, Kernel and QEMU sets.
- Dirty pages bitmap is queried from IOMMU container rather than from
vendor driver for per device. Added 2 ioctls to achieve this.
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
- 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
- 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
Kirti Wankhede (15):
vfio: KABI for migration interface for device state
vfio iommu: Add ioctl defination to get dirty pages bitmap.
vfio iommu: Add ioctl defination to unmap IOVA and return dirty bitmap
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 vfio_listener_log_sync to mark dirty pages
vfio: Add ioctl to get dirty pages bitmap during dma unmap.
vfio: Make vfio-pci device migration capable.
hw/vfio/Makefile.objs | 2 +-
hw/vfio/common.c | 188 ++++++++++-
hw/vfio/migration.c | 717 ++++++++++++++++++++++++++++++++++++++++++
hw/vfio/pci.c | 206 ++++++++++--
hw/vfio/pci.h | 1 -
hw/vfio/trace-events | 19 ++
include/hw/vfio/vfio-common.h | 19 ++
linux-headers/linux/vfio.h | 164 ++++++++++
8 files changed, 1291 insertions(+), 25 deletions(-)
create mode 100644 hw/vfio/migration.c
- [PATCH v9 Qemu 00/15] Add migration support for VFIO devices,
Kirti Wankhede <=
- [PATCH v9 QEMU 01/15] vfio: KABI for migration interface for device state, Kirti Wankhede, 2019/11/12
- [PATCH v9 QEMU 02/15] vfio iommu: Add ioctl defination to get dirty pages bitmap., Kirti Wankhede, 2019/11/12
- [PATCH v9 QEMU 03/15] vfio iommu: Add ioctl defination to unmap IOVA and return dirty bitmap, Kirti Wankhede, 2019/11/12
- [PATCH v9 QEMU 04/15] vfio: Add function to unmap VFIO region, Kirti Wankhede, 2019/11/12
- [PATCH v9 QEMU 05/15] vfio: Add vfio_get_object callback to VFIODeviceOps, Kirti Wankhede, 2019/11/12
- [PATCH v9 QEMU 06/15] vfio: Add save and load functions for VFIO PCI devices, Kirti Wankhede, 2019/11/12
- [PATCH v9 QEMU 07/15] vfio: Add migration region initialization and finalize function, Kirti Wankhede, 2019/11/12
- [PATCH v9 QEMU 08/15] vfio: Add VM state change handler to know state of VM, Kirti Wankhede, 2019/11/12