virtualbox.org

On the vbox toolbar, the little icon with the 'V' called "Additional Feature Status", there is an item called 'Unrestricted Execution'. It says "disabled". What exactly is this? I don't see anything in the User Manual that explains it. I would have thought it is the same thing as 'Execution Cap' which says "100%"; but apparently not. Should it be enabled? How do I do that if it should be? What are the advantages/disadvantages of having it set enabled vs. disabled?

Well I started looking around the webs to see if I could find an answer and the most relevant one is from a discussion from last year. In particular:

michaln wrote:That is especially true with VT-x implementations without unrestricted execution support (basically CPUs older than Sandy Bridge generation) because in those cases, the hypervisor has to emulate quite a few instructions. Even with unrestricted execution, emulated hardware devices still need to run on the host (whether in userland or in the kernel) and need access to all of the guest's memory.

So, I guess it's got to do with some CPUs and their support for specific features. It seems that there is a switch to turn it on or off via the VBoxManage command line program, but I don't know anything more than that...

VBoxManage modifyvm --vtxux on|off

User Manual, Ch. 8.8.1 wrote:• --vtxux on|off: If hardware virtualization is enabled, for Intel VT-x only, this setting enables or disables the use of the unrestricted guest mode feature for executing your guest.

RonSMeyer1 wrote:On the vbox toolbar, the little icon with the 'V' called "Additional Feature Status", there is an item called 'Unrestricted Execution'. It says "disabled". What exactly is this? I don't see anything in the User Manual that explains it. I would have thought it is the same thing as 'Execution Cap' which says "100%"; but apparently not. Should it be enabled? How do I do that if it should be? What are the advantages/disadvantages of having it set enabled vs. disabled?

That little pop-up can be misleading sometimes... several of the features it shows can be disabled or enabled by user but also may or may not be present in hardware. All those features are enabled by default, so if you didn't change any setting and the pop-up shows "disabled", it means the feature is not supported by your CPU.

The short answer is that other than getting a newer CPU, there's nothing you can do. That said, unrestricted execution makes little difference for modern operating systems, which is why it took Intel several years to implement it. AMD's hardware virtualization had an equivalent feature from the very beginning.