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

[Xiang Zheng]

Thank you very much, Kirti and Yan!

On 2020/5/18 11:36, Yan Zhao wrote:
> On Mon, May 18, 2020 at 10:39:52AM +0800, 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/
>>
> I just updated the patches to v4.
> https://patchwork.kernel.org/cover/11554617/.
> 
> It's based on v17 kernel + v16 qemu with some minor changes in qemu.
> 
>> However, I cannot find the detailed implementation about device state
>> saving/restoring and dirty page logging. Has i40e hardware already supported
>> these two features?
>>
> In v4, vendor driver for i40e vf reports dirty pages to vfio container.
> the detailed implementation of identifying dirty pages and device state
> is not sent yet for process reason.
> We use a software way to get dirty pages i.e. dynamically trapping of BAR 0.

Sounds interesting, is the dirty pages tracking done in the VM's vf driver or
in the host's vf-migration module? It seems done in the host side, but I still
cannot understand how dynamically trapping of BAR 0 can track the dirty pages.

> 
> Thanks
> Yan
>> 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 <address@hidden> 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
>>
> 
> .
> 

-- 
Thanks,
Xiang