Re: [PATCH Kernel v21 0/8] Add UAPIs to support migration for VFIO devices

Xiang Zheng
2020-05-18T02:40:06Z

Hi Kirti and Yan,

How can I test this patch series on my SR-IOV devices?
I have looked through Yan's pathes for i40e VF live migration support：
https://patchwork.kernel.org/patch/11375177/

However, I cannot find the detailed implementation about device state
saving/restoring and dirty page logging. Has i40e hardware already supported
these two features?

And if once a device supports both features, how to implement live
migration for this device via this series patch?

On 2020/5/16 5:13, Kirti Wankhede 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.
>
> Adding revision history from previous QEMU patch set to understand KABI
> changes done till now
>
> 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 | 569 ++++++++++++++++++++++++++++++++++++----
> include/linux/vfio.h | 4 +-
> include/uapi/linux/vfio.h | 315 ++++++++++++++++++++++
> 4 files changed, 842 insertions(+), 59 deletions(-)
>

--
Thanks,
Xiang