KB 2885465: CPU resources are not allocated correctly for VMs on Windows Server 2012

Bug #1 Fixed in KB2885465

When a VM CPU limit is set to 15 percent or less of the total CPU resources on the computer, the VM crashes.
Note This issue does not occur when the virtual machine is running Windows 8, Windows Server 2012, or a later version of Windows.

This issue occurs because the timer clock interrupts are not sent to the virtual machine in time. Therefore, the virtual machine assumes that a hardware error occurred.

Bug #2 Fixed in KB2885465

VMs are allocated less CPU resources than the limit that you configured. For example, if you set the CPU limit on a virtual machine to 20 percent of CPU resources on the computer, the virtual machine is allocated less than 20 percent of CPU resources.

This happens because the hypervisor throttles the resources that are provided to the virtual machine.

Download the fix here: http://support.microsoft.com/kb/2885465