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Ready for Testing: Updated Tech Preview with Big Sur Support

At WWDC 2020, the good folks at Apple wow’d us with a look at the next major version of macOS: 11.0 Big Sur, and it’s no stretch for us to say: We’re pleasantly impressed.

We’ve been working to update Fusion with support for the new rendition of macOS, and today we’re pleased to share with you some early progress with the introduction of a new Tech Preview.

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Big Changes

Big Sur brings with it some really big visual changes, but also major changes under the hood. For instance, Apple has been progressively deprecating 3rd party Kernel Extensions or “kexts” which Fusion needs to run VMs and containers. In order to continue to operate in this model, we’ve re-architected our hypervisor stack to leverage Apple’s native hypervisor APIs, allowing us to run VMs without any kernel extensions.¬†

On macOS Catalina systems, Fusion operates as it always has using kernel extensions to provide functionality. However on Big Sur systems, Fusion operates entirely without kexts.

This Tech Preview is the first release of us operating in this new mode and we’re eager to hear your feedback.

This Tech Preview supports macOS Big Sur 11.0 Beta 2 for both Host and Guest. For example, you can run Big Sur VMs on macOS Catalina, as well as on Big Sur hosts.

What else is in this preview?

Building on the last previews, this TP includes DX11 and OpenGL 4.1 support, as well as eGPU support for improved graphics performance. For example, you can render DX11 graphics for Windows VMs on the built-in display for a MacBook Air using an eGPU housing a Radeon 5700. The performance gains vs. a discrete mobile GPU are pretty significant! One might even say ‘YUUUGE’. (In order to use your eGPU, you must select ‘Prefer eGPU’ from the Virtual Machine > Settings > Display window. This is a per-VM feature.)

We’re also deprecating macOS 10.14 Mojave hosts, starting with this tech preview. Fusion 11.5.x will be the last version of Fusion which supports 10.14, whereas this year’s major release will support 10.15 and 11.0.

How to provide feedback?

We would love to hear from you in our Fusion Beta community: https://communities.vmware.com/community/vmtn/beta/fusion-pro

Known Issues

With such big changes under the hood, there are of course some known issues that we’re working on, both with our code as well as filing issues with Apple directly.

  • Nested VMs are not currently supported.
  • Jumbo Frames feature currently does not function
  • When the installation of a macOS¬†Big Sur guest completes, the virtual disk containing the temporary installer image is not automatically deleted.
    • Workaround: Manually delete the disk once installation is complete
  • Big Sur guests may log out unexpectedly and/or display a black screen when clicking an invisible icon in the upper right corner of the display.
    • Workaround: There is no workaround at this time, we are continuing to investigate
  • A powered-on VM snapshotted or suspended with Fusion running on a macOS 10.15.x or earlier host might fail to resume on a macOS Big Sur host.
    • Worksaround: Power Off your VMs before upgrading your host to Big Sur to avoid VM corruption. As always, employ backups when testing beta software!
  • A maximum of 31 vCPUs are available when running on the current seed of macOS 11 Big Sur. Configuring 32 vCPUs will prompt an error message to reduce the number of cores to 31 or less. (this is temporary and not related to licensing)
    • Workaround: Use 31 or fewer vCPU cores
  • REST API is now only available to local connections.
  • VMs that have side channel mitigations enabled while running on Fusion on macOS 11 Big Sur may have reduced performance. This setting is enabled by default.
    • Side channel attacks allow unauthorized read access by malicious processes or virtual machines to the contents of protected kernel or host memory. CPU vendors have introduced a number of features to protect data against this class of attacks such as indirect branch prediction barriers, single thread indirect branch predictor mode, indirect branch restricted speculation mode and L1 data cache flushing. While these features are effective at preventing side channel attacks they can cause noticeable performance degradation in some cases.
    • Workaround: If your security situation allows, you may regain some performance by disabling side channel mitigations. in your VM Settings > Advanced window.
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About Michael Roy

Michael Roy is the Product Line Manager for Desktop Hypervisor products such as VMware Fusion and Workstation.