On Fri, Aug 02, 2019 at 05:05:56PM +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 v1: > - add new QMP events, > - one is send when the primary device is unplugged > - one is send when VIRTIO_NET_F_STANDBY is not negotiated. > This is needed because we hide the primary device until > the feature bit is negotiated and then add it with > qdev_add_device(). The event is for libvirt to be aware of that. > - patch 7/9: a new migration state, called wait-unplug. > It is entered after SETUP and before ACTIVE. In this phase we check > devices for pending guest unplug complete event. > This patch still has a problem. It checks in a loop if there are still > devices that are not unplugged by the guest. If the guest never > returns it will run forever. How to terminate this loop? I thought > about a timed wait semaphore or just spinning for a certain amount of time, > but nothing seems good. Any ideas here? > - patch 2/9: When unplugging the primary devices, only do the guest part i.e. > call hotplug_handler_unplug_request() which calls the pcie attention > button code. The unrealize part is not done so the ressources of the > device are not freed. In case of migration failure we can re-plug the > device to > the guest with hotplug_handler_hotplug(). I tested migration failure and > a following second attempt to migrate that doesn't fail. > - add the primary device on the target VM, done in runstate change > handler. > - fix error reporting (dgilbert) > - get rid of timer to add device after feature negotiation > > 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 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 3 and 4 make sure that we can unplug the vfio-device before > migration starts > > * 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 adds a new migration state that is entered while we wait for > devices to be unplugged by guest OS > > * Patch 8 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 9 sets the pending_deleted_event before triggering the guest > unplug request > > 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 > > 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 NIC and was able to migrate the VM with > above mentioned workarounds for open problems. > > Command line example: > > qemu-system-x86_64 -enable-kvm -m 3072 -smp 3 \ > -machine q35,kernel-irqchip=split -cpu host \ > -k fr \ > -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,standby=net1 \ > /root/rhel-guest-image-8.0-1781.x86_64.qcow2
Didn't read this yet, one question: how do migration commands look like? > I'm grateful for any remarks or ideas! > > Thanks! > > Changes from RFCv2 to v1: > - work around circular dependency of commandline options. Just add > failover=on to the virtio-net standby options and reference it from > primary (vfio-pci) device with standby=<id> > - add patch 3/4 to allow migration of vfio-pci device when it is part of a > failover pair, still disallow for all other devices > - add patch 4/4 to allow unplug of device during migrationm, make an > exception for failover primary devices. I'd like feedback on how to > solve this more elegant. I added a boolean to DeviceState, have it > default to false for all devices except for primary devices. > - not tested yet with surprise removal > - I don't expect this to go in as it is, still needs more testing but > I'd like to get feedback on above mentioned changes. > > > > Jens Freimann (9): > qdev/qbus: Add hidden device support > net/virtio: add failover support > vfio: unplug failover primary device before migration > migration: allow unplug during migration for failover devices > qapi: add unplug primary event > qapi: Add failover negotiated event > migration: Add new migration state wait-unplug > pci: mark devices partially unplugged > pci: mark device having guest unplug request pending > > hw/core/qdev.c | 20 ++++ > hw/net/virtio-net.c | 180 +++++++++++++++++++++++++++++++++ > hw/pci/pci.c | 2 + > hw/pci/pcie.c | 6 ++ > hw/vfio/pci.c | 25 ++++- > hw/vfio/pci.h | 2 + > include/hw/pci/pci.h | 1 + > include/hw/qdev-core.h | 9 ++ > include/hw/virtio/virtio-net.h | 13 +++ > include/hw/virtio/virtio.h | 1 + > include/migration/vmstate.h | 2 + > migration/migration.c | 14 +++ > migration/savevm.c | 18 ++++ > migration/savevm.h | 1 + > qapi/migration.json | 24 ++++- > qapi/net.json | 16 +++ > qdev-monitor.c | 43 +++++++- > vl.c | 6 +- > 18 files changed, 375 insertions(+), 8 deletions(-) > > -- > 2.21.0