Re: [PATCH Kernel v24 0/8] Add UAPIs to support migration for VFIO devices

[Stefan Hajnoczi]

On Fri, May 29, 2020 at 02:00:46AM +0530, Kirti Wankhede wrote:
> * 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.

From what I can tell only the iommu participates in dirty page tracking.
This places the responsibility for dirty page tracking on IOMMUs. My
understanding is that support for dirty page tracking is currently not
available in IOMMUs.

Can a PCI device implement its own DMA dirty log and let an mdev driver
implement the dirty page tracking using this mechanism? That way we
don't need to treat all pinned pages as dirty all the time.

Stefan

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