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

Kirti Wankhede
2020-05-18T03:18:17Z

On 5/18/2020 8:09 AM, Xiang Zheng wrote:
> 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.

Details of device state transitions, how user application should use
UAPI and how vendor driver should behave are mentioned in the comment of
UAPI:
https://lore.kernel.org/kvm/1589577203-20640-2-git-send-email-kwankhede@nvidia.com/

> 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?
>

Here is the patch-set which adds migration support to mtty sample
device, you can refer to see how to implement on driver side:
https://lore.kernel.org/kvm/1588614860-16330-1-git-send-email-kwankhede@nvidia.com/

I'm working on preparing QEMU patches for v21 and will be sending out soon.

Thanks,
Kirti

> 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(-)
>>
>