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

Yan Zhao
2020-05-18T03:46:53Z

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.

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 <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
>