On Mon, Nov 04, 2024 at 12:21:24PM +0200, Yishai Hadas wrote: > This series enhances the vfio-virtio driver to support live migration > for virtio-net Virtual Functions (VFs) that are migration-capable. > > This series follows the Virtio 1.4 specification to implement the > necessary device parts commands, enabling a device to participate in the > live migration process. > > The key VFIO features implemented include: VFIO_MIGRATION_STOP_COPY, > VFIO_MIGRATION_P2P, VFIO_MIGRATION_PRE_COPY. > > The implementation integrates with the VFIO subsystem via vfio_pci_core > and incorporates Virtio-specific logic to handle the migration process. > > Migration functionality follows the definitions in uapi/vfio.h and uses > the Virtio VF-to-PF admin queue command channel for executing the device > parts related commands. virtio things here: Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx> Alex, your tree I presume? I hope the virtio changes do not cause conflicts. > Patch Overview: > The first four patches focus on the Virtio layer and address the > following: > - Define the layout of the device parts commands required as part of the > migration process. > - Provide APIs to enable upper layers (e.g., VFIO, net) to execute the > related device parts commands. > > The last three patches focus on the VFIO layer: > - Extend the vfio-virtio driver to support live migration for Virtio-net > VFs. > - Move legacy I/O operations to a separate file, which is compiled only > when VIRTIO_PCI_ADMIN_LEGACY is configured, ensuring that live > migration depends solely on VIRTIO_PCI. > > Additional Notes: > - The kernel protocol between the source and target devices includes a > header containing metadata such as record size, tag, and flags. > The record size allows the target to read a complete image from the > source before passing device part data. This follows the Virtio > specification, which mandates that partial device parts are not > supplied. The tag and flags serve as placeholders for future extensions > to the kernel protocol between the source and target, ensuring backward > and forward compatibility. > > - Both the source and target comply with the Virtio specification by > using a device part object with a unique ID during the migration > process. As this resource is limited to a maximum of 255, its lifecycle > is confined to periods when live migration is active. > > - According to the Virtio specification, a device has only two states: > RUNNING and STOPPED. Consequently, certain VFIO transitions (e.g., > RUNNING_P2P->STOP, STOP->RUNNING_P2P) are treated as no-ops. When > transitioning to RUNNING_P2P, the device state is set to STOP and > remains STOPPED until it transitions back from RUNNING_P2P->RUNNING, at > which point it resumes its RUNNING state. During transition to STOP, > the virtio device only stops initiating outgoing requests(e.g. DMA, > MSIx, etc.) but still must accept incoming operations. > > - Furthermore, the Virtio specification does not support reading partial > or incremental device contexts. This means that during the PRE_COPY > state, the vfio-virtio driver reads the full device state. This step is > beneficial because it allows the device to send some "initial data" > before moving to the STOP_COPY state, thus reducing downtime by > preparing early and warming-up. As the device state can be changed and > the benefit is highest when the pre copy data closely matches the final > data we read it in a rate limiter mode and reporting no data available > for some time interval after the previous call. With PRE_COPY enabled, > we observed a downtime reduction of approximately 70-75% in various > scenarios compared to when PRE_COPY was disabled, while keeping the > total migration time nearly the same. > > - Support for dirty page tracking during migration will be provided via > the IOMMUFD framework. > > - This series has been successfully tested on Virtio-net VF devices. > > Changes from V0: > https://lore.kernel.org/kvm/20241101102518.1bf2c6e6.alex.williamson@xxxxxxxxxx/T/ > > Vfio: > Patch #5: > - Enhance the commit log to provide a clearer explanation of P2P > behavior over Virtio devices, as discussed on the mailing list. > Patch #6: > - Implement the rate limiter mechanism as part of the PRE_COPY state, > following Alex’s suggestion. > - Update the commit log to include actual data demonstrating the impact of > PRE_COPY, as requested by Alex. > Patch #7: > - Update the default driver operations (i.e., vfio_device_ops) to use > the live migration set, and expand it to include the legacy I/O > operations if they are compiled and supported. > > Yishai > > Yishai Hadas (7): > virtio_pci: Introduce device parts access commands > virtio: Extend the admin command to include the result size > virtio: Manage device and driver capabilities via the admin commands > virtio-pci: Introduce APIs to execute device parts admin commands > vfio/virtio: Add support for the basic live migration functionality > vfio/virtio: Add PRE_COPY support for live migration > vfio/virtio: Enable live migration once VIRTIO_PCI was configured > > drivers/vfio/pci/virtio/Kconfig | 4 +- > drivers/vfio/pci/virtio/Makefile | 3 +- > drivers/vfio/pci/virtio/common.h | 127 +++ > drivers/vfio/pci/virtio/legacy_io.c | 420 +++++++++ > drivers/vfio/pci/virtio/main.c | 500 ++-------- > drivers/vfio/pci/virtio/migrate.c | 1336 +++++++++++++++++++++++++++ > drivers/virtio/virtio_pci_common.h | 19 +- > drivers/virtio/virtio_pci_modern.c | 457 ++++++++- > include/linux/virtio.h | 1 + > include/linux/virtio_pci_admin.h | 11 + > include/uapi/linux/virtio_pci.h | 131 +++ > 11 files changed, 2594 insertions(+), 415 deletions(-) > create mode 100644 drivers/vfio/pci/virtio/common.h > create mode 100644 drivers/vfio/pci/virtio/legacy_io.c > create mode 100644 drivers/vfio/pci/virtio/migrate.c > > -- > 2.27.0
