On 8/25/20 8:56 AM, Michal Privoznik wrote: There is one exception to this - if the device to be migrated is the VF of an SRIOV-capable network card, then there is machinery in qemu to automatically unplug the device before migration starts, and then automatically plug in a new similar device on the other end after the guest has started there. This all works in concert with a virtio-net emulated network device that is bonded together in the guest (linux only) to provide a single network device in the guest - when the VF is visible and working, it will be preferred for all traffic, but if the VF is missing then the virtio-net emulated device will be used. The result is that under normal operation the vfio-assigned VF is used for all network traffic, but during migration when the VF has been unplugged, the virtio-net device is used, so there is no disruption in network traffic, just a bit of degraded performance during migration. Here is a description of how this is configured in a libvirt domain definition: https://www.libvirt.org/formatdomain.html#teaming-a-virtio-hostdev-nic-pair This is all fairly new, and unfortunately doesn't work properly for all SRIOV cards.

On 8/26/20 8:27 AM, Erik Skultety wrote: Yeah that. That reminds me that at one of KVM Forums I've seen a demo of migration with a PCI device plugged in whole time, but it was all experimental. /me goes and tries to find it. à voilà: https://www.youtube.com/watch?v=ZAzv0c-fdAc Michal