Hey,
Presented herewith a series based on the basic VFIO migration protocol v2
implementation [1].
It is split from its parent series[5] to solely focus on device dirty
page tracking. Device dirty page tracking allows the VFIO device to
record its DMAs and report them back when needed. This is part of VFIO
migration and is used during pre-copy phase of migration to track the
RAM pages that the device has written to and mark those pages dirty, so
they can later be re-sent to target.
Device dirty page tracking uses the DMA logging uAPI to discover device
capabilities, to start and stop tracking, and to get dirty page bitmap
report. Extra details and uAPI definition can be found here [3].
Device dirty page tracking operates in VFIOContainer scope. I.e., When
dirty tracking is started, stopped or dirty page report is queried, all
devices within a VFIOContainer are iterated and for each of them device
dirty page tracking is started, stopped or dirty page report is queried,
respectively.
Device dirty page tracking is used only if all devices within a
VFIOContainer support it. Otherwise, VFIO IOMMU dirty page tracking is
used, and if that is not supported as well, memory is perpetually marked
dirty by QEMU. Note that since VFIO IOMMU dirty page tracking has no HW
support, the last two usually have the same effect of perpetually
marking all pages dirty.
Normally, when asked to start dirty tracking, all the currently DMA
mapped ranges are tracked by device dirty page tracking. If using a
vIOMMU we block live migration. It's temporary and a separate series is
going to add support for it. Thus this series focus on getting the
ground work first.
The series is organized as follows:
- Patches 1-7: Fix bugs and do some preparatory work required prior to
adding device dirty page tracking.
- Patches 8-10: Implement device dirty page tracking.
- Patch 11: Blocks live migration with vIOMMU.
- Patches 12-13 enable device dirty page tracking and document it.
Comments, improvements as usual appreciated.