Now that the driver supports live migration, only the legacy IO
functionality depends on config VIRTIO_PCI_ADMIN_LEGACY.
As part of that we introduce a bool configuration option as a sub menu
under the driver's main live migration feature named
VIRTIO_VFIO_PCI_ADMIN_LEGACY, to control the legacy IO functionality.
This will let users configuring the kernel, know which features from the
description might be available in the resulting driver.
As of that, move the legacy IO into a separate file to be compiled only
once CONFIG_VIRTIO_VFIO_PCI_ADMIN_LEGACY was configured and let the live
migration depends only on VIRTIO_PCI.
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20241113115200.209269-8-yishaih@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Add PRE_COPY support for live migration.
This functionality may reduce the downtime upon STOP_COPY as of letting
the target machine to get some 'initial data' from the source once the
machine is still in its RUNNING state and let it prepares itself
pre-ahead to get the final STOP_COPY data.
As 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.
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.
This means we avoid reading new data from the device for a specified
time interval after the last read.
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.
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20241113115200.209269-7-yishaih@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Add support for basic live migration functionality in VFIO over
virtio-net devices, aligned with the virtio device specification 1.4.
This includes the following VFIO features:
VFIO_MIGRATION_STOP_COPY, VFIO_MIGRATION_P2P.
The implementation registers with the VFIO subsystem using vfio_pci_core
and then incorporates the virtio-specific logic for the migration
process.
The migration follows the definitions in uapi/vfio.h and leverages the
virtio VF-to-PF admin queue command channel for execution device parts
related commands.
Additional Notes:
-----------------
The kernel protocol between the source and target devices contains a
header with metadata, including record size, tag, and flags.
The record size allows the target to recognize and read a complete image
from the source before passing the device part data. This adheres to the
virtio device specification, which mandates that partial device parts
cannot be supplied.
The tag and flags serve as placeholders for future extensions of the
kernel protocol between the source and target, ensuring backward and
forward compatibility.
Both the source and target comply with the virtio device specification
by using a device part object with a unique ID as part of the migration
process. Since this resource is limited to a maximum of 255, its
lifecycle is confined to periods with an active live migration flow.
According to the virtio specification, a device has only two modes:
RUNNING and STOPPED. As a result, certain VFIO transitions (i.e.,
RUNNING_P2P->STOP, STOP->RUNNING_P2P) are treated as no-ops. When
transitioning to RUNNING_P2P, the device state is set to STOP, and it
will remain STOPPED until the transition out of RUNNING_P2P->RUNNING, at
which point it returns to RUNNING. During transition to STOP, the virtio
device only stops initiating outgoing requests(e.g. DMA, MSIx, etc.) but
still must accept incoming operations.
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20241113115200.209269-6-yishaih@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
