OpenBSD-current now runs as guest under Apple Hypervisor

319 pointsposted 11 hours ago
by gpi
(undeadly.org)

32 Comments

Fiveplus

9 hours 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

2 hours 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.)

patjensen

9 hours 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 minutes ago

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

my123

10 hours ago

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

tannhaeuser

5 hours ago

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

m132

4 hours 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.

atmosx

2 hours 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.

cpach

7 hours ago

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

carlm42

2 hours 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!

MillionOClock

7 hours 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?

TacticalCoder

38 minutes 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

10 hours ago

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

eschaton

10 hours 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

7 hours ago

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

eschaton

7 hours 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

4 hours ago

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

eschaton

4 hours 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?

fooker

3 hours ago

I had to implement system calls in xv6.

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

glhaynes

3 hours 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.

eschaton

3 hours ago

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

cpach

7 hours 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.

eschaton

7 hours 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.

Rediscover

7 hours 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

6 hours 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.

fragmede

6 hours 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.

ggm

6 hours 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

5 hours 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!

iberator

9 hours ago

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