After the Hyper-V role is installed , When you try to create a new virtual machine, it fails to start with the following error:
The virtual machine could not be started because the hypervisor is not running.
Cause: Hardware virtualization or DEP was disabled in the BIOS.
Resolution: Enable Hardware virtualization or DEP in the BIOS. In some cases, the server needs to be physically shutdown in order for the new BIOS settings to take effect.
What is the DEP ?!!! Data Execution Prevention (DEP) is a set of hardware and software technologies that perform additional checks on memory to help protect against malicious code exploits.
Hardware-enforced DEP marks all memory locations in a process as non-executable unless the location explicitly contains executable code. One kind of malicious code attacks tries to insert and run code from non-executable memory locations. DEP helps prevent these attacks by intercepting them and raising an exception.
Hardware-enforced DEP
Hardware-enforced DEP marks all memory locations in a process as non-executable unless the location explicitly contains executable code. A class of attacks exists that tries to insert and run code from non-executable memory locations. DEP helps prevent these attacks by intercepting them and raising an exception.
Hardware-enforced DEP relies on processor hardware to mark memory with an attribute that indicates that code should not be executed from that memory. DEP functions on a per-virtual memory page basis, and DEP typically changes a bit in the page table entry (PTE) to mark the memory page.
Processor architecture determines how DEP is implemented in hardware and how DEP marks the virtual memory page. However, processors that support hardware-enforced DEP can raise an exception when code is executed from a page that is marked with the appropriate attribute set.
Advanced Micro Devices (AMD) and Intel have defined and shipped Windows-compatible architectures that are compatible with DEP.
Beginning with Windows XP SP2, the 32-bit version of Windows uses one of the following:
· The no-execute page-protection (NX) processor feature as defined by AMD.
· The Execute Disable Bit (XD) feature as defined by Intel.
To use these processor features, the processor must be running in Physical Address Extension (PAE) mode. However, Windows will automatically enable PAE mode to support DEP. Users do not have to separately enable PAE by using the /PAE boot switch.
Note: Because 64-bit kernels are Address Windowing Extensions (AWE) aware, there is not a separate PAE kernel in 64-bit versions of Windows.
For more information about PAE and AWE in Windows Server 2003, click the following article number to view the article in the Microsoft Knowledge Base:
283037 (http://support.microsoft.com/kb/283037/ ) Large memory support is available in Windows Server 2003 and in Windows 2000
Benefits
The primary benefit of DEP is that it helps prevent code execution from data pages, such as the default heap pages, various stack pages, and memory pool pages. Typically, code is not executed from the default heap and the stack. Hardware-enforced DEP detects code that is running from these locations and raises an exception when execution occurs. If the exception is unhandled, the process will be stopped. Execution of code from protected memory in kernel mode causes a Stop error.
DEP can help block a class of security intrusions. Specifically, DEP can help block a malicious program in which a virus or other type of attack has injected a process with additional code and then tries to run the injected code. On a system with DEP, execution of the injected code causes an exception. Software-enforced DEP can help block programs that take advantage of exception-handling mechanisms in Windows.
For more information Check Microsoft KBs
http://support.microsoft.com/kb/912923
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