Re: [PATCH Kernel v24 0/8] Add UAPIs to support migration for VFIO devices

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 29 May 2020 02:00:46 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> Hi,
> 
> This patch set adds:
> * IOCTL VFIO_IOMMU_DIRTY_PAGES 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 IOMMU capable device is present in the
>   container and all pages are pinned and mapped, then all pages are marked
>   dirty.
>   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 should be considered
>   as dirty.
>   This ioctl is also used to start/stop dirty pages tracking for pinned and
>   unpinned pages while migration is active.
> 
> * Updated IOCTL VFIO_IOMMU_UNMAP_DMA 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.
> 
> * Patch 8 detect if IOMMU capable device driver is smart to report pages
>   to be marked dirty by pinning pages using vfio_pin_pages() API.
> 
> 
> 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.
> 
> v23 -> v24
> - Fixed nit picks by Cornelia
> - Fixed warning reported by test robot.

Applied to my next branch for v5.8.  Thanks for your persistence and
for everyone's participation!  Thanks,

Alex

> v22 -> v23
> - Fixed issue reported by Yan
> https://lore.kernel.org/kvm/97977ede-3c5b-c5a5-7858-7eecd7dd531c@nvidia.com/
> - Fixed nit picks suggested by Cornelia
> 
> v21 -> v22
> - Fixed issue raised by Alex :
> https://lore.kernel.org/kvm/20200515163307.72951dd2@w520.home/
> 
> v20 -> v21
> - Added checkin for GET_BITMAP ioctl for vfio_dma boundaries.
> - Updated unmap ioctl function - as suggested by Alex.
> - Updated comments in DIRTY_TRACKING ioctl definition - as suggested by
>   Cornelia.
> 
> v19 -> v20
> - Fixed ioctl to get dirty bitmap to get bitmap of multiple vfio_dmas
> - Fixed unmap ioctl to get dirty bitmap of multiple vfio_dmas.
> - Removed flag definition from migration capability.
> 
> v18 -> v19
> - Updated migration capability with supported page sizes bitmap for dirty
>   page tracking and  maximum bitmap size supported by kernel module.
> - Added patch to calculate and cache pgsize_bitmap when iommu->domain_list
>   is updated.
> - Removed extra buffers added in previous version for bitmap manipulation
>   and optimised the code.
> 
> v17 -> v18
> - Add migration capability to the capability chain for VFIO_IOMMU_GET_INFO
>   ioctl
> - Updated UMAP_DMA ioctl to return bitmap of multiple vfio_dma
> 
> v16 -> v17
> - Fixed errors reported by kbuild test robot <lkp@intel.com> on i386
> 
> v15 -> v16
> - Minor edits and nit picks (Auger Eric)
> - On copying bitmap to user, re-populated bitmap only for pinned pages,
>   excluding unmapped pages and CPU dirtied pages.
> - Patches are on tag: next-20200318 and 1-3 patches from Yan's series
>   https://lkml.org/lkml/2020/3/12/1255
> 
> v14 -> v15
> - Minor edits and nit picks.
> - In the verification of user allocated bitmap memory, added check of
>    maximum size.
> - Patches are on tag: next-20200318 and 1-3 patches from Yan's series
>   https://lkml.org/lkml/2020/3/12/1255
> 
> v13 -> v14
> - Added struct vfio_bitmap to kabi. updated structure
>   vfio_iommu_type1_dirty_bitmap_get and vfio_iommu_type1_dma_unmap.
> - All small changes suggested by Alex.
> - Patches are on tag: next-20200318 and 1-3 patches from Yan's series
>   https://lkml.org/lkml/2020/3/12/1255
> 
> v12 -> v13
> - Changed bitmap allocation in vfio_iommu_type1 to per vfio_dma
> - Changed VFIO_IOMMU_DIRTY_PAGES ioctl behaviour to be per vfio_dma range.
> - Changed vfio_iommu_type1_dirty_bitmap structure to have separate data
>   field.
> 
> v11 -> v12
> - Changed bitmap allocation in vfio_iommu_type1.
> - Remove atomicity of ref_count.
> - Updated comments for migration device state structure about error
>   reporting.
> - Nit picks from v11 reviews
> 
> v10 -> v11
> - Fix pin pages API to free vpfn if it is marked as unpinned tracking page.
> - Added proposal to detect if IOMMU capable device calls external pin pages
>   API to mark pages dirty.
> - Nit picks from v10 reviews
> 
> v9 -> v10:
> - Updated existing VFIO_IOMMU_UNMAP_DMA ioctl to get dirty pages bitmap
>   during unmap while migration is active
> - Added flag in VFIO_IOMMU_GET_INFO to indicate driver support dirty page
>   tracking.
> - If iommu_mapped, mark all pages dirty.
> - Added unpinned pages tracking while migration is active.
> - Updated comments for migration device state structure with bit
>   combination table and state transition details.
> 
> 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 (8):
>   vfio: UAPI for migration interface for device state
>   vfio iommu: Remove atomicity of ref_count of pinned pages
>   vfio iommu: Cache pgsize_bitmap in struct vfio_iommu
>   vfio iommu: Add ioctl definition for dirty pages tracking
>   vfio iommu: Implementation of ioctl for dirty pages tracking
>   vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap
>   vfio iommu: Add migration capability to report supported features
>   vfio: Selective dirty page tracking if IOMMU backed device pins pages
> 
>  drivers/vfio/vfio.c             |  13 +-
>  drivers/vfio/vfio_iommu_type1.c | 572 ++++++++++++++++++++++++++++++++++++----
>  include/linux/vfio.h            |   4 +-
>  include/uapi/linux/vfio.h       | 319 ++++++++++++++++++++++
>  4 files changed, 849 insertions(+), 59 deletions(-)
>