VT-x setting cannot be disabled if VT-x is not supported

[CoJaBo]

The option to turn VT-x on or off is only shown if VT-x is supported by the host CPU. This makes it impossible to use a VM created on a VT-x capable machine on another machine that does not support VT-x; when attempting to start such a machine, VirtualBox complains that VT-x is not supported, but there is no way to turn it off. Additionally, turning off the VT-x related settings through the command line does not appear to work either; there is no error, but the settings do not get changed.

1. Create a VM on a machine that supports VT-x; make sure VT-x is enabled (which appears to be the default)
2. Export the VM; in my case, it was to a .OVA file.
3. Set the machine on fire (optional)
4. Import the VM on another machine that does not support VT-x
5. Attempt to start the VM

The only work-around I could find was to re-create the machine from scratch, using only the existing virtual disks; this results in loss of snapshot data though. The VM booted up just fine after this, without VT-x support. Suposedly, editing the XML files also works, but this does not appear possible with .OVA format VMs.

Rather than outright disabling access to the VT-x settings when not supported, the GUI ought to just mark them invalid like every other settings page does; this would allow the problem to be corrected.

Importing the machine on a VT-x machine and disabling it there ought to work, of course, but in my case I did not have access to any other machine that supported it. The same issue also happens when downloading VMs created by others.

[Frank Mehnert]

From your description it rather seems that your VM really requires VT-x. This happens if one of the following conditions is true:

• the VM uses more than one guest CPU
• the VM runs a 64-bit guest

If neither of these conditions is true, VirtualBox will automatically start the VM in non-VT-x mode, even if VT-x is enabled in the VM settings.

If this is not true, please attach a VBox.log file from such a VM session which you imported and which did not start because of the missing VT-x feature.

[aeichner]

Please reopen if still relevant with a recent VirtualBox release.