[PATCH v4 0/11] add failover feature for assigned network devices

[Jens Freimann <jfreimann@redhat.com>]

This is implementing the host side of the net_failover concept
(https://www.kernel.org/doc/html/latest/networking/net_failover.html)

Changes since v3:
* Patch 1,  make return values of qdev_should_hide_device() more clear
* Patch 1,  clarify comment about new should_be_hidden DeviceListener
* Patch 2   new patch, add net_failover_option_id to PCIDevice, only
            allow PCIExpress devices for now 
* Patch 8,  only go into wait_unplug state when failover devices are present
* Patch 8,  add new state to migration_is_setup_or_active, tested cancelling
            while migration is in this state
* Patch 8,  simplify handling of wait_unplug state, don't cancel migration after
            timeout, let upper layer do this, get rid of retry counter (dgilbert)
* Patch 11, move net_failover_pair_id to PCIDev, move check for pci class
            to PCI code, only allow PCIe devices for now as we only support
            hotplugging these devices (aw)
* verified qemu make check tests ran, checked that docker-test-quick@centos7 runs
  successful, tested migration with/without failover, without vfio-pci 
* this now allows only PCIe devices because that's the only hotplug
  controller that supports the partial unplug as of now. I'll work on 
  making it discoverable for libvirt or on support for the
  other hotplug controllers in a follow-on patch set
 
The general idea is that we have a pair of devices, a vfio-pci and a
virtio-net device. Before migration the vfio device is unplugged and data
flows to the virtio-net device, on the target side another vfio-pci device
is plugged in to take over the data-path. In the guest the net_failover
module will pair net devices with the same MAC address.

* Patch 1 adds the infrastructure to hide the device for the qbus and qdev APIs

* Patch 2 adds checks to PCIDevice for only allowing ethernet devices as
  failover primary and only PCIExpress capable devices

* Patch 3 sets a new flag for PCIDevice 'partially_hotplugged' which we
  use to skip the unrealize code path when doing a unplug of the primary
  device

* Patch 4 sets the pending_deleted_event before triggering the guest
  unplug request

* Patch 5 and 6 add new qmp events, one sends the device id of a device
  that was just requested to be unplugged from the guest and another one
  to let libvirt know if VIRTIO_NET_F_STANDBY was negotiated

* Patch 7 make sure that we can unplug the vfio-device before
  migration starts

* Patch 8 adds a new migration state that is entered while we wait for
  devices to be unplugged by guest OS

* Patch 9 just adds the new migration state to a check in libqos code

* Patch 10 In the second patch the virtio-net uses the API to defer adding the vfio
  device until the VIRTIO_NET_F_STANDBY feature is acked. It also
  implements the migration handler to unplug the device from the guest and
  re-plug in case of migration failure

* Patch 11 allows migration for failover vfio-pci devices

Previous discussion:
  RFC v1 https://patchwork.ozlabs.org/cover/989098/
  RFC v2 https://www.mail-archive.com/qemu-devel@nongnu.org/msg606906.html
  v1: https://lists.gnu.org/archive/html/qemu-devel/2019-05/msg03968.html
  v2: https://www.mail-archive.com/qemu-devel@nongnu.org/msg635214.html
  v3: https://patchew.org/QEMU/20191011112015.11785-1-jfreimann@redhat.com/

To summarize concerns/feedback from previous discussion:
1.- guest OS can reject or worse _delay_ unplug by any amount of time.
  Migration might get stuck for unpredictable time with unclear reason.
  This approach combines two tricky things, hot/unplug and migration.
  -> We need to let libvirt know what's happening. Add new qmp events
     and a new migration state. When a primary device is (partially)
     unplugged (only from guest) we send a qmp event with the device id. When
     it is unplugged from the guest the DEVICE_DELETED event is sent.
     Migration will enter the wait-unplug state while waiting for the guest
     os to unplug all primary devices and then move on with migration.
2. PCI devices are a precious ressource. The primary device should never
  be added to QEMU if it won't be used by guest instead of hiding it in
  QEMU.
  -> We only hotplug the device when the standby feature bit was
     negotiated. We save the device cmdline options until we need it for
     qdev_device_add()
     Hiding a device can be a useful concept to model. For example a
     pci device in a powered-off slot could be marked as hidden until the slot is
     powered on (mst).
3. Management layer software should handle this. Open Stack already has
  components/code to handle unplug/replug VFIO devices and metadata to
  provide to the guest for detecting which devices should be paired.
  -> An approach that includes all software from firmware to
     higher-level management software wasn't tried in the last years. This is
     an attempt to keep it simple and contained in QEMU as much as possible.
     One of the problems that stopped management software and libvirt from
     implementing this idea is that it can't be sure that it's possible to
     re-plug the primary device. By not freeing the devices resources in QEMU
     and only asking the guest OS to unplug it is possible to re-plug the
     device in case of a migration failure.
4. Hotplugging a device and then making it part of a failover setup is
   not possible
  -> addressed by extending qdev hotplug functions to check for hidden
     attribute, so e.g. device_add can be used to plug a device.


I have tested this with a mlx5 and igb NIC and was able to migrate the VM.

Command line example:

qemu-system-x86_64 -enable-kvm -m 3072 -smp 3 \
        -machine q35,kernel-irqchip=split -cpu host   \
        -serial stdio   \
        -net none \
        -qmp unix:/tmp/qmp.socket,server,nowait \
        -monitor telnet:127.0.0.1:5555,server,nowait \
        -device pcie-root-port,id=root0,multifunction=on,chassis=0,addr=0xa \
        -device pcie-root-port,id=root1,bus=pcie.0,chassis=1 \
        -device pcie-root-port,id=root2,bus=pcie.0,chassis=2 \
        -netdev tap,script=/root/bin/bridge.sh,downscript=no,id=hostnet1,vhost=on \
        -device virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:6f:55:cc,bus=root2,failover=on \
	-device vfio-pci,host=5e:00.2,id=hostdev0,bus=root1,net_failover_pair_id =net1 \
        /root/rhel-guest-image-8.0-1781.x86_64.qcow2

I'm grateful for any remarks or ideas!

Thanks!

regards,
Jens 


Jens Freimann (10):
  qdev/qbus: add hidden device support
  pci: mark devices partially unplugged
  pci: mark device having guest unplug request pending
  qapi: add unplug primary event
  qapi: add failover negotiated event
  migration: allow unplug during migration for failover devices
  migration: add new migration state wait-unplug
  libqos: tolerate wait-unplug migration state
  net/virtio: add failover support
  vfio: unplug failover primary device before migration

 hw/core/qdev.c                 |  20 +++
 hw/net/virtio-net.c            | 267 +++++++++++++++++++++++++++++++++
 hw/pci/pci.c                   |   2 +
 hw/pci/pcie.c                  |   6 +
 hw/vfio/pci.c                  |  35 ++++-
 hw/vfio/pci.h                  |   2 +
 include/hw/pci/pci.h           |   1 +
 include/hw/qdev-core.h         |  10 ++
 include/hw/virtio/virtio-net.h |  12 ++
 include/hw/virtio/virtio.h     |   1 +
 include/migration/vmstate.h    |   2 +
 migration/migration.c          |  34 +++++
 migration/migration.h          |   3 +
 migration/savevm.c             |  36 +++++
 migration/savevm.h             |   1 +
 qapi/migration.json            |  24 ++-
 qapi/net.json                  |  16 ++
 qdev-monitor.c                 |  43 +++++-
 tests/libqos/libqos.c          |   3 +-
 vl.c                           |   6 +-
 20 files changed, 515 insertions(+), 9 deletions(-)

-- 
2.21.0

*** BLURB HERE ***

Jens Freimann (11):
  qdev/qbus: add hidden device support
  pci: add option for net failover
  pci: mark devices partially unplugged
  pci: mark device having guest unplug request pending
  qapi: add unplug primary event
  qapi: add failover negotiated event
  migration: allow unplug during migration for failover devices
  migration: add new migration state wait-unplug
  libqos: tolerate wait-unplug migration state
  net/virtio: add failover support
  vfio: unplug failover primary device before migration

 hw/core/qdev.c                 |  24 +++
 hw/net/virtio-net.c            | 282 +++++++++++++++++++++++++++++++++
 hw/pci/pci.c                   |  17 ++
 hw/pci/pcie.c                  |   6 +
 hw/vfio/pci.c                  |  26 ++-
 hw/vfio/pci.h                  |   1 +
 include/hw/pci/pci.h           |   4 +
 include/hw/qdev-core.h         |   9 ++
 include/hw/virtio/virtio-net.h |  12 ++
 include/hw/virtio/virtio.h     |   1 +
 include/migration/vmstate.h    |   2 +
 migration/migration.c          |  22 +++
 migration/migration.h          |   3 +
 migration/savevm.c             |  36 +++++
 migration/savevm.h             |   1 +
 qapi/migration.json            |  24 ++-
 qapi/net.json                  |  16 ++
 qdev-monitor.c                 |  38 ++++-
 tests/libqos/libqos.c          |   3 +-
 vl.c                           |   6 +-
 20 files changed, 519 insertions(+), 14 deletions(-)

-- 
2.21.0


Jens Freimann (11):
  qdev/qbus: add hidden device support
  pci: add option for net failover
  pci: mark devices partially unplugged
  pci: mark device having guest unplug request pending
  qapi: add unplug primary event
  qapi: add failover negotiated event
  migration: allow unplug during migration for failover devices
  migration: add new migration state wait-unplug
  libqos: tolerate wait-unplug migration state
  net/virtio: add failover support
  vfio: unplug failover primary device before migration

 hw/core/qdev.c                 |  24 +++
 hw/net/virtio-net.c            | 282 +++++++++++++++++++++++++++++++++
 hw/pci/pci.c                   |  17 ++
 hw/pci/pcie.c                  |   6 +
 hw/vfio/pci.c                  |  26 ++-
 hw/vfio/pci.h                  |   1 +
 include/hw/pci/pci.h           |   4 +
 include/hw/qdev-core.h         |   9 ++
 include/hw/virtio/virtio-net.h |  12 ++
 include/hw/virtio/virtio.h     |   1 +
 include/migration/vmstate.h    |   2 +
 migration/migration.c          |  21 +++
 migration/migration.h          |   3 +
 migration/savevm.c             |  36 +++++
 migration/savevm.h             |   2 +
 qapi/migration.json            |  24 ++-
 qapi/net.json                  |  16 ++
 qdev-monitor.c                 |  38 ++++-
 tests/libqos/libqos.c          |   3 +-
 vl.c                           |   6 +-
 20 files changed, 519 insertions(+), 14 deletions(-)

-- 
2.21.0

Jens Freimann (11):
  qdev/qbus: add hidden device support
  pci: add option for net failover
  pci: mark devices partially unplugged
  pci: mark device having guest unplug request pending
  qapi: add unplug primary event
  qapi: add failover negotiated event
  migration: allow unplug during migration for failover devices
  migration: add new migration state wait-unplug
  libqos: tolerate wait-unplug migration state
  net/virtio: add failover support
  vfio: unplug failover primary device before migration

 hw/core/qdev.c                 |  24 +++
 hw/net/virtio-net.c            | 282 +++++++++++++++++++++++++++++++++
 hw/pci/pci.c                   |  17 ++
 hw/pci/pcie.c                  |   6 +
 hw/vfio/pci.c                  |  31 +++-
 hw/vfio/pci.h                  |   1 +
 include/hw/pci/pci.h           |   4 +
 include/hw/qdev-core.h         |   9 ++
 include/hw/virtio/virtio-net.h |  12 ++
 include/hw/virtio/virtio.h     |   1 +
 include/migration/vmstate.h    |   2 +
 migration/migration.c          |  21 +++
 migration/migration.h          |   3 +
 migration/savevm.c             |  36 +++++
 migration/savevm.h             |   2 +
 qapi/migration.json            |  24 ++-
 qapi/net.json                  |  16 ++
 qdev-monitor.c                 |  38 ++++-
 tests/libqos/libqos.c          |   3 +-
 vl.c                           |   6 +-
 20 files changed, 524 insertions(+), 14 deletions(-)

-- 
2.21.0