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Comment by andix | Hacker News Reader

Doesn't Windows do it more or less the same?

A lot of Windows features depend on Hyper-V, once enabled Windows is not booted directly any more, Hyper-V is started and the main Windows system runs in a privileged VM.

All other VMs need to utilize the Hyper-V hypervisor, because nested virtualization is not that well supported. So even VMware then is just a front-end for Hyper-V.

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Back when I ran Windows in a KVM VM for gaming, a lot of anti-cheat systems didn't take kindly to running in a virtualized environment.

Turning on HyperV to go KVM->HyperV->Windows effectively 'laundered' my VM signature enough to satisfy the anticheats, though the overall perf hit was ~10-15%.

Very interesting. I wonder what sort of (available) CPU would be ideal for such a setup. A 7800x3D or 7950x. Also, was there any hit on the GPU side?

Yeah I'm very curious as to how this effected 99% framerates and frame pacing.

I suspect only a modest hit to average framerate, but I can only imagine it hurt the actual max frametimes which make it "feel choppy" even if the framerate is still higher then your monitor's refresh rate.

More cache never hurts. I'd imagine there were GPU perf gaps, though they were hard to distinguish from CPU-based performance hits. The most notable issues were random latency spikes caused by the multiple layers of hypervisors, which interfered with some games and occasionally caused audio/video desync on Youtube.

I ultimately tore down that setup and just swapped to dual-boot. The steps needed to set up high-performance VFIO (i.e. clearing enough contiguous RAM for 1GB Hugepages) meant most of the benefits of VFIO never really materialized for me.

You are right that Windows itself runs under Hyper-V as a guest when virtualisation-based security is enabled and it even has paravirtual devices that are not massively different to VirtIO.

I think your statement about VMware Workstation is right as of today too with recent versions, although for a long time older versions would simply refuse to start if it detected that Hyper-V was enabled, presumably because it made assumptions about the host virtualisation support.

It's not just security features that need Hyper-V. Also WSL (Linux on Windows) or the Android Subsystem (run any side loaded app or anything from the Amazon App Store) need Hyper-V. Both of them are super useful for me, more and more things are iOS/Android App based only. Linux should speak for itself.

Only WSLv2 needs (or uses) Hyper-V.

But WSL1 is de-facto dead, although it is still supported.

It still makes more sense than v2 for certain patterns.

I still use WSL1 daily. It makes a lot more sense than WSL2 for me. If I want a VM of Linux, I’ll run a VM of Linux. The exciting thing about WSL from the beginning was the notion of actually running Linux processes in Windows without a VM.

Is it possible to use hyper v directly? Like could I boot into linux but switch over to Windows with just a key press? I'm guessing no since its not in Microsoft interest to do so

Not with Hyper-V but the thing to be aware of is there is no difference which you initially “boot into” since each is essentially run at the same level.

You can install ESXi (free) to do what you are asking, though.

ESXi is a completely headless system, except some minimal management UI/CLI there is no possibility to directly interact with the VMs on the host system. At least that's my understanding.

And I think a very similar thing can be archived with Windows Server Core. Running Hyper-V with just a minimal Windows installation for management, without the full Windows UI.

Yeah, but it's configurable. I have it pull up the core on a VGA card and then boot up my primary VM on a GPU.

That's an interesting idea, to run Hyper-V completely without Windows. I think it's not possible, at least not without some substantial amount of hacking.

But it's no problem to run Linux on Hyper-V. It's a hypervisor, off course you can start nearly any operating system as a VM. You can also give the VM access to some hardware components. But I don't think it's possible to get a full native Linux desktop experience, with GPU/Screen, Keyboard and Mouse connected to the host system.

Edit: this post seems to answer your question, not sure if it's correct: https://superuser.com/a/1531799

You can soon run Linux on Hyper-V without Windows: https://www.theregister.com/2021/02/17/linux_as_root_partiti...

It’s been a few years now, I wonder how far this project has gotten

> A lot of Windows features depend on Hyper-V, once enabled Windows is not booted directly any more, Hyper-V is started and the main Windows system runs in a privileged VM.

Got a source for this? Not that I don't believe you but other than for the Xbox I haven't seen/can't find any details about this.

Surprised you didn’t find the information, it’s covered in details in Microsoft own docs: https://learn.microsoft.com/en-us/virtualization/hyper-v-on-...

quote:

“ In addition, if you have Hyper-V enabled, those latency-sensitive, high-precision applications may also have issues running in the host. This is because with virtualization enabled, the host OS also runs on top of the Hyper-V virtualization layer, just as guest operating systems do. However, unlike guests, the host OS is special in that it has direct access to all the hardware, which means that applications with special hardware requirements can still run without issues in the host OS.”

From https://learn.microsoft.com/en-us/virtualization/hyper-v-on-...

"Virtualization-Based Security: Enabled by Default"

https://techcommunity.microsoft.com/t5/virtualization/virtua...

> Hyper-V is started and the main Windows system runs in a privileged VM.

What are the performance implications of that?

Minor performance loss. 5% fps on average. MS recommends turning it off if gaming is your primary use.

Even then it's really not that much of a hit if you have half-decent hardware, I've kept it on and I think the only issue I saw was launch day BG3 and it would use much more power from the wall than when I turned it off.

Make sure to have Intel VT-x or AMD-V enabled too.

There are now a lot of BIOS flags that you can have set to off by default that'll silently hinder performance.

There's no way in hell to run any relatively modern hypervisor without VT-x or AMD-V. There are other, newer additions that do provide a performance boost (or well, a smaller loss) but yeah, VT-x/AMD-V is the basis.

> Hyper-V is started and the main Windows system runs in a privileged VM

Wait it's all VMs? Always has been?! That is actual one sentence horror.

Sometimes it's hard to tell how many VMs there are between my code and the actual hardware. It seems to be VMs all the way down.

It hasn't always been, nor is it necessarily now. If you enable Hyper-V, that will act as Hypervisor for your machine and boot Windows by default. Applications that use it (VMWare, for instance, or Microsoft ones like WSL2) will add their own guests to the Hypervisor.

It is not the default configuration. And it wasn't even installed before Windows 8.

Isn't virtualization based security the default for Windows 11? I only have upgraded Win 11 systems, so no idea what's the default on a fresh installation.

My fresh install of Windows 11 definitely didn't have Hyper-V active by default. It had to install it and reboot to activate the WSL2 subsystem.

Now, to be fair, this was an install from a couple major updates back. So newer builds might have it active by default.

It is on some hardware on latest feature updates.

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