PCI passthrough causes Skylake/Z170 system not to boot

Fri Mar 4 20:51:17 UTC 2016

I opened a but for this already[1], but I figured I'd ask here to see if
anyone's encountered it before.

I have a FreeBSD 10.3-BETA2 system with a Skylake CPU and a Z170
motherboard that stops booting when I try to use PCI passthrough. After the
boot loarder runs, but before root is mounted, an interrupt storm causes
controllers/devices (including the root disk) to be disconnected and
reconnected. Then, the system isn't able to mount the root disk, and the
boot fails. Disabling VT-d, removing vmm_load from loader.conf, and
removing pptdevs from loader.conf all fix the booting issue, but those are
all needed for PCI passthrough.

I've reproduced this with different devices, but the report is PCI
passthrough of the onboard ethernet controller.

[1]: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=207602