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[v9,Kernel,0/5] Add KABIs to support migration for VFIO devices

Message ID 1573578220-7530-1-git-send-email-kwankhede@nvidia.com
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Series Add KABIs to support migration for VFIO devices | expand

Message

Kirti Wankhede Nov. 12, 2019, 5:03 p.m. UTC 
Hi Alex,

To keep kernel and QEMU patches in sync, keeping v9 version for this patch
set. Till v8 version, KABI was being discussed from QEMU patch series[1].
In earlier version mail and as per in person discussion at KVM forum, this
patch set adds:
* New IOCTL VFIO_IOMMU_GET_DIRTY_BITMAP to get dirty pages bitmap with
  respect to IOMMU container rather than per device. 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.
* New IOCTL VFIO_IOMMU_UNMAP_DMA_GET_BITMAP to get dirty pages bitmap
  before unmapping IO virtual address range.
  With vIOMMU, during pre-copy phase of migration, while CPUs are still
  running, IO virtual address unmap can happen while device still keeping
  reference of guest pfns. Those pages should be reported as dirty before
  unmap, so that VFIO user space application can copy content of those
  pages from source to destination.

Yet TODO:
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 such that vendor
driver could report dirty pages to VFIO module during migration phases.

[1] https://www.mail-archive.com/qemu-devel@nongnu.org/msg640400.html

Adding revision history from previous QEMU patch set to understand KABI
changes done till now

v8 -> v9:
- Split patch set in 2 sets, Kernel and QEMU.
- 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
  get_dirty_pages routines.
- Skip called get_dirty_pages routine for mapped MMIO region of device.
- Added trace events.
- Split 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 (5):
  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 iommu: Implementation of ioctl to get dirty pages bitmap.
  vfio iommu: Implementation of ioctl to get dirty bitmap before unmap

 drivers/vfio/vfio_iommu_type1.c | 163 ++++++++++++++++++++++++++++++++++++++-
 include/uapi/linux/vfio.h       | 164 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 325 insertions(+), 2 deletions(-)