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

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

On 2018-06-27 07:06:42 +0300, Michael S. Tsirkin wrote:
> 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.

Could you please elaborate?

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 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
> 
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