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.
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.
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.
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 \
/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