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Re: [PATCH v6 0/11] add failover feature for assigned network devices


From: Jens Freimann
Subject: Re: [PATCH v6 0/11] add failover feature for assigned network devices
Date: Mon, 28 Oct 2019 11:27:23 +0100
User-agent: NeoMutt/20180716-1376-5d6ed1

Hi Michael,

I addressed all comments and feedback and think this can be merged but
I'm unclear about which tree it should go to. Will you merge it into
the virtio-tree?

regards,
Jens

On Fri, Oct 25, 2019 at 02:19:19PM +0200, Jens Freimann wrote:
This is implementing the host side of the net_failover concept
(https://www.kernel.org/doc/html/latest/networking/net_failover.html)

Changes since v5:
* rename net_failover_pair_id parameter/property to failover_pair_id
* in PCI code use pci_bus_is_express(). This won't fail on functions > 0
* make sure primary and standby can't be added to same PCI slot
* add documentation file in docs/ to virtio-net patch, add file to
  MAINTAINERS (added to networking devices section)
* add comment to QAPI event for failover negotiation, try to improve
  commit message

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/address@hidden/msg606906.html
 v1: https://lists.gnu.org/archive/html/qemu-devel/2019-05/msg03968.html
 v2: https://www.mail-archive.com/address@hidden/msg635214.html
 v3: https://patchew.org/QEMU/address@hidden/
 v4: https://patchew.org/QEMU/address@hidden/
 v5: https://patchew.org/QEMU/address@hidden/

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,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 (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

MAINTAINERS                    |   1 +
docs/virtio-net-failover.rst   |  68 ++++++++
hw/core/qdev.c                 |  25 +++
hw/net/virtio-net.c            | 302 +++++++++++++++++++++++++++++++++
hw/pci/pci.c                   |  32 ++++
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         |  30 ++++
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                  |  19 +++
qdev-monitor.c                 |  43 ++++-
tests/libqos/libqos.c          |   3 +-
vl.c                           |   6 +-
22 files changed, 652 insertions(+), 15 deletions(-)
create mode 100644 docs/virtio-net-failover.rst

--
2.21.0






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