RE: [PATCH v12 Kernel 0/7] KABIs to support migration for VFIO devices

[Zengtao (B)]

Hi Kirti:

What kind of platform/IO are you using now to do the basic code
verification?

I just want to check if I can verify it on my platform, and if any open
IO cards available? 

Thanks.

Regards
Zengtao 

> -----Original Message-----
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> On Behalf Of Kirti Wankhede
> Sent: Saturday, February 08, 2020 3:42 AM
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> address@hidden; address@hidden; Kirti Wankhede
> Subject: [PATCH v12 Kernel 0/7] KABIs to support migration for VFIO
> devices
> 
> Hi,
> 
> This patch set adds:
> * New 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 7 is proposed change to 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.
> 
> Adding revision history from previous QEMU patch set to understand
> KABI
> changes done till now
> 
> 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 (7):
>   vfio: KABI for migration interface for device state
>   vfio iommu: Remove atomicity of ref_count of pinned pages
>   vfio iommu: Add ioctl definition for dirty pages tracking.
>   vfio iommu: Implementation of ioctl to for dirty pages tracking.
>   vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before
> unmap
>   vfio iommu: Adds flag to indicate dirty pages tracking capability
>     support
>   vfio: Selective dirty page tracking if IOMMU backed device pins pages
> 
>  drivers/vfio/vfio.c             |  13 +-
>  drivers/vfio/vfio_iommu_type1.c | 435
> +++++++++++++++++++++++++++++++++++++---
>  include/linux/vfio.h            |   4 +-
>  include/uapi/linux/vfio.h       | 267 +++++++++++++++++++++++-
>  4 files changed, 692 insertions(+), 27 deletions(-)
> 
> --
> 2.7.0