On Wed, 6 Nov 2024 04:32:31 -0500 "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > 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. Sure, I can ultimately take it through my tree once we have consensus. Yishai, please add Michael's ack to 1-4 on the next round. Thanks, Alex > > 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 >
