On Mon, Apr 08, 2019 at 10:16:50AM +0100, Dr. David Alan Gilbert wrote: > * Michael S. Tsirkin (m...@redhat.com) wrote: > > On Fri, Apr 05, 2019 at 09:56:29AM +0100, Dr. David Alan Gilbert wrote: > > > * 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 > > > > Um, during which process? Guests are gradually fixed to support > > surprise removal well. Part of it is thunderbolt which makes > > it incredibly easy. Yes - bios/grub will need to learn to > > handle this well. > > Ignoring the actual mechanism of the unplug itself; there are probably > loads of cases; e.g. > > running with both cards > hot unplug real card > start migration > guest reboots > Kernel sees only the virtio card > migration completes > hotadd the real card back > > so the guest has to know to pair the real card even though it booted > with only the virtio card.
Yes - that's why virtio has a flag to notify guest there will be a pair even if it's not there at the moment. > I'm sure there are loads of other corners. > > > > > > 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? > > > > If qemu frees up resources (as it does on unplug) then libvirt > > is not guaranteed it can roll the change back on e.g. > > migration failure. > > Can you explain this in a bit more detail please; do you mean if it > frees the netdev? > > > But really another issue is simply that it's a mechanism, > > there's no policy that management needs to decide on. > > Doing it at lowest possible level ensures all > > upper layers benefit with minimal pain. > > Network setups in things like OpenStack can be really complex and > involve interacting with switches etc - something somewhere might > have to reconfigure a switch when you pull the real card. > > Dave > > > > > > 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 > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
