Description of problem:
Using a linux-based guest with KVM (tested both CentOS 6.4 and Fedora 17 guests), rebooting the guest machine causes host to completely lock up - nothing even shown in /var/log/messages.  Occurred on previous kernel but waited for new kernel to check if it was still happening, however the trigger on the previous kernel was different.  With previous kernel, noted that one of the components in the stack trace (which managed to display) was kms_drm, however unsure if this is also the case now as no stack trace displayed and no other information available.

Version-Release number of selected component (if applicable):
kernel-3.9.5-201.fc18.x86_64 (previous)
kernel-3.9.6-200.fc18.x86_64 (current)

How reproducible:
For me, every time, though it may also be hardware-related.

Steps to Reproduce:
1. Install linux-based guest in libvirt.
2. Update guest using `yum update`
3. Reboot guest

On previous kernel, occasionally the guest would boot without incident, however could induce a similar crash through the following:
1. Boot guest to runlevel 3 (with ssh running)
2. SSH to root@guest
3. `vim` .ssh/authorized_keys

Actual results:
Host machine freezes completely, cannot switch to terminal, cannot ssh in, no output or stack trace to screen, nothing in /var/log/messages

Expected results:
Host machine to remain stable and guest machine to either handle exception itself or, preferably, work correctly.

Additional info:
As I am unable to provide full stack trace information, I understand that it would be difficult to reproduce this bug for testing; however if it may help, I can provide hardware specifications on request.