Re: [Qemu-devel] [PATCH v2 0/4] Use of unique identifier for pairing virtio and passthrough devices...

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 26, 2018 at 10:49:30PM -0500, Venu Busireddy wrote:
> 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".

There's still discussion around whether it should be
a virtio pci capability, a virtio net config field or
a new kind of capability.

> 2. Enhance the QEMU CLI to include a "uuid" option to the virtio device.
>    The "uuid" is a string in UUID format.
> 
> 3. Enhance the QEMU CLI to include a "uuid" option to the bridge device.
>    The "uuid" is a string in UUID format. Currently, PCIe bridge for
>    the Q35 model is supported.
> 
> 4. The operator creates a unique identifier string using 'uuidgen'.
> 
> 5. When the virtio device is created, the operator uses the "uuid" option
>    (for example, '-device virtio-net-pci,uuid="string"') and specifies
>    the UUID created in step 4.
> 
>    QEMU stores the UUID in the virtio device's configuration space
>    in the capability "VIRTIO_PCI_CAP_GROUP_ID_CFG".
> 
> 6. When assigning a PCI device to the guest in passthrough mode, the
>    operator first creates a bridge using the "uuid" option (for example,
>    '-device pcie-downstream,uuid="string"') to specify the UUID created
>    in step 4, and then attaches the passthrough device to the bridge.
> 
>    QEMU stores the UUID 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. To avoid mixing up with other bridges, the bridge
>    will be created with vendor ID 0x1b36 (PCI_VENDOR_ID_REDHAT) and
>    device ID 0x000e (PCI_DEVICE_ID_REDHAT_PCIE_BRIDGE) if the "uuid"
>    option is specified. Otherwise, current defaults are used.
> 
> 7. 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

The part where the visibility of a vfio device is controlled by the
virtio driver acknowledging the backup feature is missing here.
 

> [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 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 (4):
>   Add a true or false option to the DEFINE_PROP_UUID macro.
>   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/acpi/vmgenid.c                           |   2 +-
>  hw/pci-bridge/Makefile.objs                 |   1 +
>  hw/pci-bridge/pci_bridge_dev.c              |   8 +
>  hw/pci-bridge/pcie_downstream.c             | 215 ++++++++++++++++++++
>  hw/pci-bridge/pcie_downstream.h             |  10 +
>  hw/pci/pci_bridge.c                         |  26 +++
>  hw/virtio/virtio-pci.c                      |  15 ++
>  hw/virtio/virtio-pci.h                      |   3 +-
>  include/hw/pci/pci.h                        |   3 +
>  include/hw/pci/pcie.h                       |   1 +
>  include/hw/qdev-properties.h                |   4 +-
>  include/standard-headers/linux/virtio_pci.h |   8 +
>  15 files changed, 295 insertions(+), 4 deletions(-)
>  create mode 100644 hw/pci-bridge/pcie_downstream.c
>  create mode 100644 hw/pci-bridge/pcie_downstream.h