We've had a rash of reports of kernels not booting on some Skylake based
machines recently. After working these, we've determined that a recent
Intel microcode update somehow conflicts with something in the system
firmware for these machine, causing a complete failure to boot after grub
loads the kernel.
Some of these systems have a firmware update (BIOS/UEFI) that restores
functionality even with the microcode being loaded. Other systems do not
yet at this time. If you experience a boot hang on a Skylake based
machine, you can try and determine if the microcode is at fault by
specifying 'dis_ucode_ldr' on the kernel command line. That prevents the
kernel from loading the microcode during the early boot.
The issue is mostly being tracked here:
https://bugzilla.redhat.com/show_bug.cgi?id=1353103
Some of the machines involved are:
Lenovo Thinkpad T460
Lenovo Thinkpad x260
Lenovo Yoga 260
ASUS Zenbook UX305CA
Samsung Notebook 9
josh