I enabled the creation of sys-usb on install. My laptop has an integrated SD card reader, and up until recently any plugged in SD cards were directly handled by dom0. But now they get handled by sys-net instead. Regular USB devices still seem to get handled properly by sys-usb however.
Does anyone have a clue what might have happened? Where I can start looking?
Seems like Qubes is using these XX_00.0 values to uniquely identify PCI devices when figuring out which qube they should map to. Seems like an unwanted side-effect to me. Just something I have to think about in the future, I guess.
To fix it I went into the Qube settings for sys-net and removed 02:00.0 from the device list.
I consider this a bug and a bit of a scary one as well:
Removing a PCI device should not cause other PCI devices to become attached to random VMs. In fact this can make entire Qubes OS installations unusable just from device removal (imagine an USB controller with keyboard to be assigned to another VM…).