[Qemu-devel] [PATCH v3 0/3] Use of unique identifier for pairing virtio and passthrough devices...

[Venu Busireddy <venu.busireddy@oracle.com>]

The patch set "Enable virtio_net to act as a standby for a passthru
device" [1] deals with live migration of guests that use passthrough
devices. However, that scheme uses the MAC address for pairing
the virtio device and the passthrough device. The thread "netvsc:
refactor notifier/event handling code to use the failover framework"
[2] discusses an alternate mechanism, such as using an UUID, for pairing
the devices. Based on that discussion, proposals "Add "Group Identifier"
to virtio PCI capabilities." [3] and "RFC: Use of bridge devices to
store pairing information..." [4] were made.

The current patch set includes all the feedback received for proposals [3]
and [4]. For the sake of completeness, patch for the virtio specification
is also included here. Following is the updated proposal.

1. Extend the virtio specification to include a new virtio PCI capability
   "VIRTIO_PCI_CAP_GROUP_ID_CFG".

2. Enhance the QEMU CLI to include a "failover-group-id" option to the
   virtio device. The "failover-group-id" is a 64 bit value.

3. Enhance the QEMU CLI to include a "failover-group-id" option to the
   Red Hat PCI bridge device (support for the i440FX model).

4. Add a new "pcie-downstream" device, with the option
   "failover-group-id" (support for the Q35 model).

5. The operator creates a 64 bit unique identifier, failover-group-id.

6. When the virtio device is created, the operator uses the
   "failover-group-id" option (for example, '-device
   virtio-net-pci,failover-group-id=<identifier>') and specifies the
   failover-group-id created in step 4.

   QEMU stores the failover-group-id in the virtio device's configuration
   space in the capability "VIRTIO_PCI_CAP_GROUP_ID_CFG".

7. When assigning a PCI device to the guest in passthrough mode, the
   operator first creates a bridge using the "failover-group-id" option
   (for example, '-device pcie-downstream,failover-group-id=<identifier>')
   to specify the failover-group-id created in step 4, and then attaches
   the passthrough device to the bridge.

   QEMU stores the failover-group-id in the configuration space of the
   bridge as Vendor-Specific capability (0x09). The "Vendor" here is
   not to be confused with a specific organization. Instead, the vendor
   of the bridge is QEMU.

8. Patch 4 in patch series "Enable virtio_net to act as a standby for
   a passthru device" [1] needs to be modified to use the UUID values
   present in the bridge's configuration space and the virtio device's
   configuration space instead of the MAC address for pairing the devices.

Thanks!

Venu

[1] https://lists.oasis-open.org/archives/virtio-dev/201805/msg00156.html
[2] https://www.spinics.net/lists/netdev/msg499011.html
[3] https://lists.oasis-open.org/archives/virtio-dev/201805/msg00118.html
[4] https://lists.oasis-open.org/archives/virtio-dev/201805/msg00204.html

Changes in v3:
  - As Michael Tsirkin suggested:
    * Changed the failover group identifier from UUID to a 64-bit value.
    * Changed the command line option from "uuid" to "failover-group-id".
    * Tweaked the "pci-bridge" device's Device ID to
      PCI_DEVICE_ID_REDHAT_BRIDGE_FAILOVER.
    * Added to new device "pcie-downstream" with Device ID
      PCI_DEVICE_ID_REDHAT_DOWNPORT_FAILOVER (to support the PCIe case).
  - Changed the patch for virtio specification to reflect the above
    changes.

Changes in v2:
  - As Michael Tsirkin suggested, changed the virtio specification
    to restrict the group identifier to be a 16-byte field, presented
    entirely in the virtio device's configuration space.
  - As Michael Tsirkin suggested, instead of tweaking the ioh3420
    device with Red Hat vendor ID, create a new PCIe bridge device
    named "pcie-downstream" with Red Hat Vendor ID, and include the
    group identifier in this device.
  - Added a new patch to enhance the "pci-bridge" device to support
    the group identifier (for the i440FX model).

Venu Busireddy (3):
  Add "Group Identifier" support to virtio devices.
  Add "Group Identifier" support to Red Hat PCI bridge.
  Add "Group Identifier" support to Red Hat PCI Express bridge.

 default-configs/arm-softmmu.mak             |   1 +
 default-configs/i386-softmmu.mak            |   1 +
 default-configs/x86_64-softmmu.mak          |   1 +
 hw/pci-bridge/Makefile.objs                 |   1 +
 hw/pci-bridge/pci_bridge_dev.c              |  10 +
 hw/pci-bridge/pcie_downstream.c             | 220 ++++++++++++++++++++
 hw/pci-bridge/pcie_downstream.h             |  10 +
 hw/pci/pci_bridge.c                         |  34 +++
 hw/virtio/virtio-pci.c                      |  15 ++
 hw/virtio/virtio-pci.h                      |   3 +-
 include/hw/pci/pci.h                        |  37 ++--
 include/hw/pci/pci_bridge.h                 |   2 +
 include/hw/pci/pcie.h                       |   1 +
 include/standard-headers/linux/virtio_pci.h |   8 +
 14 files changed, 326 insertions(+), 18 deletions(-)
 create mode 100644 hw/pci-bridge/pcie_downstream.c
 create mode 100644 hw/pci-bridge/pcie_downstream.h