OpenBSD-current now runs as guest under Apple Hypervisor

408 pointsposted 23 days ago
by gpi
(undeadly.org)

64 Comments

Fiveplus

22 days ago

A good update. The VIRTIO_NET_F_MTU negotiation has been a roadblock for many guest OS implementations on apple's virtualization stack. The spec is vague enough that linux just does it while openbsd had to explicitly patch in support to handle the hypervisor's hardmtu limit.

This is a big deal for local development imho. With the raw single-thread performance of the M4/M5 chips, an openbsd guest is arguably the best environment for testing pf configurations or running isolated mail servers (for example). Being able to rely on viogpu without the black-screen-of-death means we can slowly move away from serial console-only installs for quick VMs.

Big kudos to Helg and Stefan!

eru

22 days ago

> With the raw single-thread performance of the M4/M5 chips, an openbsd guest is arguably the best environment for testing pf configurations or running isolated mail servers (for example).

A unikernel would probably be even better? (But then you need a mail server that's set up for running as a unikernel, without an underlying OS.)

wang_li

22 days ago

>Being able to rely on viogpu without the black-screen-of-death means we can slowly move away from serial console-only installs for quick VMs.

No, thanks. My IaC doesn't want or need any interaction when spinning up a quick or slow VM.

patjensen

22 days ago

The bigger news is that this also fixes the QEMU compatibility bug that makes OpenBSD hang out of the box on arm64 when starting X.

It started in 7.3 with the frame buffer changes and the only workaround was to disable the kernel driver.

Maybe more people will get to try out OpenBSD successfully now.

someguyiguess

22 days ago

I am one of them! Been wanting to try it out for a while but my only available machine is an MBP

patjensen

21 days ago

I can confirm it is fixed in the latest OpenBSD snapshot build. Works great.

archy_

22 days ago

Why does QEMU need to start X? Shouldn't that be OpenBSD's responsibility?

codys

22 days ago

OpenBSD does start X. And subsequently OpenBSD apparently hangs (or did so previously) when OpenBSD was running under Qemu.

The subject in the parent comment changed to OpenBSD when they mentioned it, and it appears you may have overlooked the subject change.

user

22 days ago

[deleted]

danwills

22 days ago

[flagged]

fleshmonad

22 days ago

Maybe not posting such comments would increase the value of this site.

my123

22 days ago

Note that this is about Virtualization.framework (Apple's first party VMM). OpenBSD worked on Hypervisor.framework + qemu since a very long time.

cpach

22 days ago

Good point. The naming of those frameworks is sooo confusing. IMHO, nearly impossible to not mix them up.

carlm42

22 days ago

My mental model is that each of these covers a different layer of the stack, from lowest to highest:

* hypervisor-framework handles the hypervisor bits, like creating virtual machines, virtualising hardware resources, basically a C API on top of Apple's hypervisor

* virtualization-framework is a higher-level API, meant to make it easy to run a full-blown VM with an OS and hardware integration, without having to reinvent the integration with lower-level primitives that hypervisor-framework provides

* containerization-framework uses virtualization-framework to run Linux containers on macOS in microVMs.

By analogy to not mix them up, it's a bit like KVM > QEMU > containerd.

Hope this helps!

Angostura

22 days ago

Well, it help me. So thanks!

tannhaeuser

22 days ago

Out of my depth here. Is that the one Tahoe was introducing? What did it solve that was impossible before?

m132

22 days ago

Virtualization.framework was introduced in Big Sur. It builds on top of Hypervisor.framework and is essentially Apple's QEMU (in some ways quite literally, it implements QEMU's pvpanic protocol for example). Before QEMU and other VMMs gained ARM64 Hypervisor.framework support, it was the only way to run virtual machines on ARM Macs and still is the only official way to virtualize ARM macOS.

The new Tahoe framework you're probably thinking of is Containerization, which is a WSL2-esque wrapper around Virtualization.framework allowing for easy installation of Linux containers.

archy_

22 days ago

>a WSL2-esque wrapper around Virtualization.framework allowing for easy installation of Linux containers.

So Linux is now a first class citizen on both Windows and Mac? I guess it really is true that 'if you can't beat em, join em.' Jobs must be rolling in his grave.

trentnelson

22 days ago

I mean to be fair, WSL1 and WSL2 are extremely successful engineering efforts by Microsoft. I can’t imagine having to go back to the Cygwin days.

freedomben

22 days ago

I'm one of the few I think who really liked Cygwin. Far from perfect of course, but I even still prefer it to WSL depending on what I'm doing.

atmosx

22 days ago

Oh good point. I mixed it up, UTM is using qemu under hood, but as someone mentioned now OpenBSD snapshot boots with qemu seemlesly. It's still virtualised though.

irusensei

22 days ago

It can also use the apple native hypervisor.

atmosx

22 days ago

Tried it earlier using UTM and the Apple hypervisor but didn’t boot.

MillionOClock

22 days ago

Maybe I am missing something but the last few times I tested VMs it seemed to end up never shrinking in RAM size once it had grown, is this a real issue and if so is there any improvement coming on that front?

daneel_w

22 days ago

You're missing the complexity of making the guest inform the host that it has fully freed this and that slab of memory and that the host may reclaim it until further notice. It's a bit more complicated than the other way around, where the guest believes it has e.g. 4 GiB of RAM available but the host doesn't allocate all of it for the guest until it tries to read/write there. A virtual machine is something entirely else than a containerized piece of software.

TacticalCoder

22 days ago

> Maybe I am missing something but the last few times I tested VMs ...

Tested VMs on what? For VMs are used daily and there are, what, hundreds of millions of VMs running as we speak? Billions?

SomaticPirate

22 days ago

Is there a guide on how to do this? I haven’t ever used the raw hypervisor.

eschaton

22 days ago

It should just be a matter of producing a kernel and, if necessary, RAM disk that can be booted the same way as Linux.

jonhohle

22 days ago

“just” is doing a lot of work in that sentence.

eschaton

22 days ago

Yes and no; kernels aren’t magic, and “change how this kernel is loaded to match how Linux does it” is actually a reasonable first assignment for an Operating Systems class at a top-tier school. (You’re basically just creating an alternative `main()` if you don’t need a RAM disk image from which to load drivers.)

fooker

22 days ago

It's a first assignment if you are talking about a computer from 1990.

eschaton

22 days ago

What, pray tell, would you do for a first assignment in an Operating Systems class at a top-tier school that actually involves making changes to on realistic operating system code?

surajrmal

22 days ago

This is the set of assignments they do at the university of Illinois (a top 10 computer engineering school): https://courses.grainger.illinois.edu/ece391/fa2025/assignme...

It looks roughly the same as when I took 15 years ago, except they switched to riscv from x86. Honestly, what you're describing sounds too difficult for a first assignment. Implementing irq handlers or syscalls on an existing codebase is far more realistic, plausible, and useful.

fooker

22 days ago

I had to implement system calls in xv6.

You can look up which top tier schools use it for OS classes.

glhaynes

22 days ago

At the risk of getting further off-topic: what sort of system calls did they have you implement? I’ve never done but a tiny bit of kernel hacking and that sounds like a good exercise, but I’m not sure what would be a good first syscall to add.

surajrmal

22 days ago

Try asking your favorite llm. They will even guide you with a small curriculum.

user

22 days ago

[deleted]

throwaway132448

22 days ago

Advice like this, and then people wonder why they’re lonely.

glhaynes

22 days ago

I don't know… people were lonely before LLMs. And, they're right, this is a question one could easily paste into a frontier model and easily get back info that's way more useful than the significant majority of blog posts or replies would give! shrug But also I'd still like to hear what fooker has to say!

eschaton

22 days ago

Oh, is that what MIT’s using these days?

cpach

22 days ago

Then one needs to launch it. Not sure if there are any lancher UIs out there, or if one has to write custom code for that.

fragmede

22 days ago

Parallels will run a VM that can (manually) boot bsd.rd from the EFI shell if you stick BOOTAA64.EFI and bsd.rd on a FAT32 GUID formatted.dmg, connect it to the VM, then boot EFI shell. Type:

    connect -r
    map -r
    fs0:
    bootaa64.efi
    boot bin.rd
Then you'll be in the OpenBSD installer, having booted an OpenBSD kernel.

You can grab the files from: https://ftp.openbsd.org/pub/OpenBSD/snapshots/arm64/

Actually installing the system is left as an exercise for the reader.

eschaton

22 days ago

My point is that as long as OpenBSD can boot like Linux, you just have to tell whatever VM front-end you’re using that you’re booting a Linux but give it an OpenBSD kernel and RAM disk.

Traditionally BSD has booted very differently than Linux, because Linus adopted the same boot process as MINIX when he first developed it (since he was actually using the MINIX boot blocks at first).

BSD has historically used a bootstrap that understands V7FS/FFS and can load a kernel from a path on it. MINIX takes the actual kernel and RAM disk images as parameters so it doesn’t need to know about filesystems, and that tradition continued with Linux bootstraps once it was standalone.

user

22 days ago

[deleted]

Rediscover

22 days ago

Who else was rdev'ing the Linux kernel to tell it where the root ext2(?) partition was long before they were using RAM disks? Like with SLS or MCC?

fragmede

22 days ago

Originally Linux had Minix FS, followed by ext. Ext2 wouldn't make an appearance until 1993 by Rémy Card, so it depends on when you were using it.

user

22 days ago

[deleted]

ggm

22 days ago

Well done! FreeBSD 15 is a complete no-go for X right now on utm, rdp/vnc is the only way. Hopefully somebody will work out how to get a frame buffer working there, from this.

infi_v12

22 days ago

This is a significant milestone for OpenBSD on Apple hardware. The improved support for Virtualization.framework will definitely make local development and testing much smoother for many users. Kudos to the developers!

6r17

22 days ago

I wonder if openbsd is secure running as a guest ? it it able to isolate it-self sufficiently so that the host cannot mathematically breach it ? (which makes openbsd very suitable for keyholding)

irusensei

22 days ago

On a slightly related note UTM remote is such a nice remote client for VMs that I wish they would make it compatible with other hypervisor protocols such as libvirtd and bhyve.

iberator

22 days ago

No X and networking. What's the point then? Useless imo

mghackerlady

22 days ago

Networking is a disappointment but OpenBSD kinda expects you to use the command line. Fire up tmux (included because they invented it) and read the god tier manpages and play some of the games that are included

cyberpunk

22 days ago

OpenBSD did not “invent” tmux afaik it was imported later.

brynet

22 days ago

tmux was my first OpenBSD port, way back in 2008, albeit it was rather short-lived.

https://marc.info/?l=openbsd-ports-cvs&m=121226747005033&w=2

I had discovered it searching on SourceForge originally, but the tmux creator Nicholas Marriott was already an OpenBSD user and he took MAINTAINER for the port.

A year later, tmux was imported by nicm@ to the OpenBSD base system, where it has remained upstream for last 16 years (GitHub sync's from OpenBSD).

https://marc.info/?l=openbsd-cvs&m=124389728412353&w=2