Virtualbox says VT-x is not available (VERR_VMX_NO_VMX). What is VT-x?

VT-x is Intel's technology for virtualization on the x86 platform. VT-x allows multiple operating systems to simultaneously share x86 processor resources in a safe and efficient manner.

Make sure Virtualization is enabled in your BIOS and that nothing uses it already - Hyper-V is a very common issue.

Please refer x86 virtualization wiki

Hope it helps :-)

If you have enabled the mode Virtualization in the BIOS and if the problem still persists, try going to

Settings -> Update & Security -> Window security -> Device security -> Core isolation details -> Turn off

and then restart the PC and try again to review the 64-bits VirtualBox environment.

To sum this up :

VT-x is not available (VERR_VMX_NO_VMX).

What is VT-x ?

VT-x is Intel's technology for virtualization on the x86 platform. VT-x allows multiple operating systems to simultaneously share x86 processor resources in a safe and efficient manner.

Possible issues & Solutions :

• VT-X is not enabled in the BIOS settings – VT-X can be disabled from the BIOS settings manually or remotely by some 3rd party applications. Solution is to enter BIOS settings at boot time and re-enable Virtualization (can be VT-x, VT-d, etc.).

• The machine’s CPU doesn’t support VT-X – Although these cases are rare, there are instances where the error is occurring because the PC in question is simply not equipped to support the VT-X technology.

• Hyper-V virtualization is enabled in Windows – This is perhaps the most common cause why this error occurs. Since Microsoft’s Hyper-V technology is known to conflict with VT-X, the OS will automatically disable VT-x if Hyper-V virtualization is enabled. You can disable it via "Turn Windows features on or off" menu in Windows settings. Note that one of "Virtual Machine Platform" and/or "Windows Hypervisor Platform" being enabled appear to cause the issue.

• Avast update disabled VT-X – As it turns out, Avast released an update that effectively disables VT-x while the real-time protection is active unless the user enables nested virtualization from the settings menu.

• Core Isolation is enabled – Core isolation is a Windows Defender Security option that is known to conflict with VT-X while it’s enabled. You can disable it from the Windows Defender options menu, or via Settings > Update & Security > Window Security > Device Security > Core Isolation Details > Turn Off

cf. other posts, most from stackexchange
"VT-x is not available" when i start my Virtual machine
https://serverfault.com/questions/620273/turn-on-virtualisation-settings-on-windows-2012-r2
https://superuser.com/questions/1266489/virtualbox-states-vt-x-is-not-available-verr-vmx-no-vmx
https://superuser.com/questions/1391838/virtual-box-is-not-working-on-windows-10
https://appuals.com/fix-vt-x-is-not-available-verr_vmx_no_vmx/

Related : VirtualBox - Kernel requires an x86-64 cpu but only detected an i686 cpu

Disable "Virtual Machine Platform" and/or "Windows Hypervisor Platform" from "Turn Windows features on or off" menu in Windows settings. After just restart and open virtual box or VMware. It works for me.

Turns out Windows has a 'Virtualization based Security Guard' which needed to be disabled. I used the powershell tool to get the job done.

.\DG_Readiness_Tool_v3.6.ps1 -Disable -AutoReboot

Here's a link to the tool:https://www.microsoft.com/en-us/download/details.aspx?id=53337

Kudos/source: https://social.technet.microsoft.com/Forums/en-US/79583454-bcd1-45a3-bc2e-a6a5078d1dde/why-is-the-hypervisor-running-even-after-i-uninstalled-hyperv?forum=win10itprovirt&prof=required

It took some time and digging to figure out it was issue only with 64-bit VMs that shows above mentioned error, and not the 32-bit VMs.

Although he doesn’t mention the actual error, the root cause of his problem is in Win 10. Hyper-V is greedy and owns the “VT-x” after booting and doesn’t share with Virtual Box at all.

Here is The two solutions:

• Either remove Hyper-V from Windows (if you’re not using it obviously) via ‘Turn Windows features on of off’

• Edit the BCD to start Windows with the Hyper-V (hypervisorlaunchtype disabled) as the post illustrates.

I suggest that If you have already enabled VTX, and checked that you have vt-d/vt-x enabled in the BIOS, try resetting the VirtualBox settings or re-installing VirtualBox: it might have nothing to do with your PC/Windows configuration.