Kabylake and Skylake bug has been discovered just one week ago. We have experiencing weird behavior on boot with this kind of processors when HT is enabled with a Supermicro X11SSV-Q and Core i7 6700 and i7 7700. This could be directly related with this Intel bug.
Problem raises when bringing up CPUs with this error:
Failed to bring up CPU 1 ( error -5 )
After one or two reboots, it manages to boot properly. But after this, sometimes some VMs hangs in a very suspicious way.
There is a microcode.dat from Intel available in that could fix this.
This microcode.dat could be included in a kernel update.