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[PATCH v27 00/17] Add migration support for VFIO devices
[PATCH v27 00/17] Add migration support for VFIO devices
Thu, 22 Oct 2020 16:41:50 +0530
This Patch set adds migration support for VFIO devices in QEMU.
This Patch set include patches as below:
- Few code refactor
- Added save and restore functions for PCI configuration space. Used
pci_device_save() and pci_device_load() so that config space cache is saved
- Generic migration functionality for VFIO device.
* This patch set adds functionality 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 zero.
- Set DIRTY_MEMORY_MIGRATION flag in dirty log mask for migration with vIOMMU
- Get migration capability from kernel module.
- Add function to start and stop dirty pages tracking.
- 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
When vIOMMU is enabled, used IOMMU notifier to get call back for mapped pages
on replay during stop-and-copy phase.
- 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.
- Added VFIO device stats to MigrationInfo
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 total 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
(RESTORE_VM, _ACTIVE, _RESUMING)
At the end, called .load_cleanup for each device and vCPUs are started.
(RUNNING, _NONE, _RUNNING)
- Migration post copy is not supported.
v26 -> 27
- Major change in Patch 3 -PCI config space save and long using VMSTATE_*
- Major change in Patch 14 - Dirty page tracking when vIOMMU is enabled using
IOMMU notifier and
its replay functionality - as suggested by Alex.
- Some Structure changes to keep all migration related members at one place.
- Pulled fix suggested by Zhi Wang <firstname.lastname@example.org>
- Add comments where even suggested and required.
v25 -> 26
- Removed emulated_config_bits cache and vdev->pdev.wmask from config space save
- Used VMStateDescription for config space save and load functionality.
- Major fixes from previous version review.
v23 -> 25
- Updated config space save and load to save config cache, emulated bits cache
and wmask cache.
- Created idr string as suggested by Dr Dave that includes bus path.
- Updated save and load function to read/write data to mixed regions, mapped or
- When vIOMMU is enabled, created mapped iova range list which also keeps
translated address. This list is used to mark dirty pages. This reduces
downtime significantly with vIOMMU enabled than migration patches from
- Removed get_address_limit() function from v23 patch as this not required now.
v22 -> v23
-- Fixed issue reported by Yan
- Sending this version to test v23 kernel version patches:
v18 -> v22
- Few fixes from v18 review. But not yet fixed all concerns. I'll address those
concerns in subsequent iterations.
- Sending this version to test v22 kernel version patches:
v16 -> v18
- Nit fixes
- Get migration capability flags from container
- Added VFIO stats to MigrationInfo
- Fixed bug reported by Yan
v9 -> v16
- KABI almost finalised on kernel patches.
- Added support for migration with vIOMMU enabled.
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 (17):
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
memory: Set DIRTY_MEMORY_MIGRATION when IOMMU is enabled
vfio: Get migration capability flags for container
vfio: Add function to start and stop dirty pages tracking
vfio: Add vfio_listener_log_sync to mark dirty pages
vfio: Dirty page tracking when vIOMMU is enabled
vfio: Add ioctl to get dirty pages bitmap during dma unmap
vfio: Make vfio-pci device migration capable
qapi: Add VFIO devices migration stats in Migration stats
hw/vfio/common.c | 449 +++++++++++++++++++-
hw/vfio/meson.build | 1 +
hw/vfio/migration.c | 935 ++++++++++++++++++++++++++++++++++++++++++
hw/vfio/pci.c | 84 +++-
hw/vfio/pci.h | 1 -
hw/vfio/trace-events | 20 +
include/hw/vfio/vfio-common.h | 24 ++
include/qemu/vfio-helpers.h | 3 +
migration/migration.c | 14 +
monitor/hmp-cmds.c | 6 +
qapi/migration.json | 17 +
softmmu/memory.c | 2 +-
12 files changed, 1512 insertions(+), 44 deletions(-)
create mode 100644 hw/vfio/migration.c
- [PATCH v27 00/17] Add migration support for VFIO devices,
Kirti Wankhede <=
- [PATCH v27 01/17] vfio: Add function to unmap VFIO region, Kirti Wankhede, 2020/10/22
- [PATCH v27 02/17] vfio: Add vfio_get_object callback to VFIODeviceOps, Kirti Wankhede, 2020/10/22
- [PATCH v27 04/17] vfio: Add migration region initialization and finalize function, Kirti Wankhede, 2020/10/22
- [PATCH v27 06/17] vfio: Add migration state change notifier, Kirti Wankhede, 2020/10/22
- [PATCH v27 07/17] vfio: Register SaveVMHandlers for VFIO device, Kirti Wankhede, 2020/10/22