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

[Michael S. Tsirkin]

I see at least comments from Markus.
You answered but don't you need to also tweak the patch?


On Mon, Oct 28, 2019 at 11:27:23AM +0100, Jens Freimann wrote:
> 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
> > 
> > 
> 
>