Given the changes in D54739, should we perhaps add an explicit disclaimer about PCI passthrough not being supported for unprivileged users?
From what I can tell, trying to run an unprivileged VM with pci passthrough won't print any warnings about not being able to open /dev/pci, and I can already see new bug reports about this.

Yes, that's a good point. I should make passthru_init() print a message when it fails due to lack of permissions.

I also realized after the fact that pci_lpc_get_sel() will fail with unprivileged bhyve, but the info it's fetching is available to unprivileged users via PCIOCGETCONF. We should rewrite that code to use PCIOCGETCONF instead.