* Jens Freimann (jfreim...@redhat.com) wrote: > ping > > FYI: I'm also working on a few related tools to detect driver behaviour when > assigning a MAC to the vf device. Code is at > https://github.com/jensfr/netfailover_driver_detect
Hi Jens, I've not been following this too uch, but: > regards, > Jens > > On Fri, Mar 22, 2019 at 02:44:45PM +0100, Jens Freimann wrote: > > This is another attempt at implementing the host side of the > > net_failover concept > > (https://www.kernel.org/doc/html/latest/networking/net_failover.html) > > > > The general idea is that we have a pair of devices, a vfio-pci and a > > emulated device. Before migration the vfio device is unplugged and data > > flows to the emulated 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. > > > > * In the first patch the infrastructure for hiding the device is added > > for the qbus and qdev APIs. A "hidden" boolean is added to the device > > state and it is set based on a callback to the standby device which > > registers itself for handling the assessment: "should the primary device > > be hidden?" by cross validating the ids of the devices. > > > > * In the second patch the virtio-net uses the API to hide the vfio > > device and unhides it when the feature is acked. > > > > Previous discussion: https://patchwork.ozlabs.org/cover/989098/ > > > > 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 can surprise-remove the PCI device and in QEMU we can do all > > necessary rollbacks transparent to management software. Will it be > > easy, probably not. This sounds 'fun' - bonus cases are things like what happens if the guest gets rebooted somewhere during the process or if it's currently sitting in the bios/grub/etc > > 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). Are they really that precious? Personally it's not something I'd worry about. > > 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. > > 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. > > > > There are still some open issues: > > > > Migration: I'm looking for something like a pre-migration hook that I > > could use to unplug the vfio-pci device. I tried with a migration > > notifier but it is called to late, i.e. after migration is aborted due > > to vfio-pci marked unmigrateable. I worked around this by setting it > > to migrateable and used a migration notifier on the virtio-net device. Why not just let this happen at the libvirt level; then you do the hotunplug etc before you actually tell qemu anything about starting a migration? > > Commandline: There is a dependency between vfio-pci and virtio-net > > devices. One points to the other via new parameters > > primar=<primary qdev id> and standby='<standby qdev id>'. This means > > that the primary device needs to be specified after standby device on > > the qemu command line. Not sure how to solve this. > > > > Error handling: Patches don't cover all possible error scenarios yet. > > > > 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,primary=hostdev0 > > \ > > -device vfio-pci,host=5e:00.2,id=hostdev0,bus=root1,standby=net1 \ Yes, that's a bit grim; it's circular dependency on the 'hostdev0' and 'net1' id's. cc'ing in Markus. Dave > > /root/rhel-guest-image-8.0-1781.x86_64.qcow2 > > > > I'm grateful for any remarks or ideas! > > > > Thanks! > > > > regards, > > Jens > > > > Sameeh Jubran (2): > > qdev/qbus: Add hidden device support > > net/virtio: add failover support > > > > hw/core/qdev.c | 27 ++++++++++ > > hw/net/virtio-net.c | 95 ++++++++++++++++++++++++++++++++++ > > hw/pci/pci.c | 1 + > > include/hw/pci/pci.h | 2 + > > include/hw/qdev-core.h | 8 +++ > > include/hw/virtio/virtio-net.h | 7 +++ > > qdev-monitor.c | 48 +++++++++++++++-- > > vl.c | 7 ++- > > 8 files changed, 189 insertions(+), 6 deletions(-) > > > > -- > > 2.20.1 > > > > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
