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How to Disable side-channel mitigations in VMWare Player

You can disable side-channel mitigations in VMWare Player to improve Windows 11 performance. VMWare Player, a free version of VMWare Workstation Pro, recently received software TPM support, allowing users to create Windows 11-compatible virtual machines for various purposes (like testing preview builds in the Windows Insider program).

VMware Player Workstation Player Screenshot

You can learn about adding TPM to a virtual machine for Windows 11 in VMWare Player in our dedicated guide.

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You might encounter one particular issue when running a Windows 11-based virtual machine in VMWare Player. The software will warn you about potential performance downgrades when using a virtual machine with side-channel mitigations.

But the problem is that VMWare Player does not provide an option to disable side-channel mitigations in the settings UI (similar to how it does not allow you to add a Trusted Platform Module inside settings for a specific VM).

Fortunately, you can fix poor performance in Windows 11 running in VMWare Player by disabling side-channel mitigations in the machine's configuration file.

Note that the message with a recommendation to disable side-channel mitigations appears only on systems with Hyper-V enabled. Learn how to enable or disable Hyper-V in Windows here.

Disable side-channel mitigations in VMWare Player

  1. Shut down your Windows 11 VM and close VMWare Player.
  2. Go to the folder where you keep your virtual machine.
  3. Enable extensions for files in Windows 11 and Windows 10, then find the VMX file (virtual machine configuration file). Open that file in Notepad.
  4. Add the following line to the list of parameters: ulm.disableMitigations="TRUE".
  5. Save changes and close Notepad.

That is how you disable side-channel mitigations in VMWare Player to fix lags in Windows 11-based virtual machines. Now you can launch your virtual machine and enjoy the restored performance.

If using Windows 11 on a virtual machine in VMWare is not your cup of tea, we have a dedicated guide about installing Windows 11 using Hyper-V. It was also possible to run Windows 11 in VirtualBox.

Unfortunately, the latter currently does not support TPM passthrough (coming soon), meaning you cannot create a Windows 11-compatible VM.

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Author: Taras Buria

Taras is here to cover stories about Microsoft and everything around, although sometimes he prefers Apple. You can stay in touch with him on Twitter.

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