r/VFIO

Demos and docs: https://zerone-laboratories.github.io/zss

Source: https://github.com/z3r0n3br4instorm/ZrnSelectiveSuspend

Maybe this is stupid

I wanted to share a side project I've been working on to solve a personal annoyance with hybrid graphics. If you've ever dealt with a discrete GPU on a laptop, you know the pain of having to log out, kill your X session, or reboot just to fully power the card down for battery, or to pass it through to a QEMU/KVM virtual machine.

I built ZrnSelectiveSuspend (ZSS) to fix that. It's an alpha tool that takes a graphics card out of service on a live Linux desktop by moving running Vulkan and OpenGL programs to another GPU while they're still drawing, then gives everything back afterwards.

**What it does right now:**

* **Zero-watt power-off:** switches the dGPU completely off under a running X session (~0.4 s) and back on (~1 s). Programs move to the iGPU and back; vkcube never stops spinning. Can also follow the charger or an idle timer.

* **Live VFIO passthrough:** `zssctl lend` moves the host's programs off the card and hands it to vfio-pci; `zssctl reclaim` power-cycles it and gives it back to the host driver with the programs returned. No reboot, no log-out. Tested with a CachyOS guest in QEMU.

Honest caveat: the guest sees the card, but nouveau stops after reading the chip ID because the Mac Edition card has no video BIOS of its own. Passing a ROM file to QEMU is next.

* **Surviving a card that vanishes:** I wrote a kernel module (ZSS_Interceptor) that notices a card losing power within ~0.1 s. If the card was idle, the driver is frozen and resumed. If a program was rendering on it, the program gets rebuilt on the iGPU in ~3.5 s with nothing lost, and `zssctl on` brings the card back in 4 - 7 s by replugging it the way NVIDIA's driver handles an unplugged eGPU. Desktop stays up the whole time. Caveat: after that rescue, the card can't be powered off or lent again until you reboot.

**What moves:** Vulkan 1.1 programs, OpenGL 3.2 programs through Mesa's Zink, Chromium and Electron apps (VS Code, Teams), and Unity games. Proton/DXVK needs Vulkan 1.3, so not yet.

**How it works, briefly:** a user-space Vulkan driver shim (ZSS_AirLock) sits between programs and the real drivers, keeps enough state to rebuild them on another GPU, and emulates missing features so Zink runs even on NVIDIA 470. A daemon sequences moves, freezes, driver suspend and power cuts. The kernel module handles PCI state, power backends and loss detection. NVIDIA additionally needs a small DKMS patch so the driver can sleep under a running display server.

**The bigger picture:**

ZSS is focused on graphics cards right now, but the long-term goal is to safely disconnect, suspend and reconnect any PCI device on a live system without taking the kernel down with it. GPUs are just the hardest place to start.

I used Claude Code a lot to build this. I made the architectural calls; it did a big share of the implementation and helped me work through the nastier kernel module and driver interactions. It's been a massive learning accelerator.

**Status:** very much alpha. Proven on one machine: a 2012 MacBook Pro (MacBookPro9,1, GT 650M + HD 4000) on Arch, kernel 7.2, X11, NVIDIA 470.256.02. Power-off currently needs an Apple gmux; an ACPI backend for most hybrid laptops since ~2015 is written but has never been run. Wayland compositors are recognised but untested. The program-moving parts are vendor-neutral and should work with any Vulkan driver.

**How you can help:** there's a tester kit that changes nothing and installs nothing. It collects what your machine has, runs the moving tests in dry-run mode, and saves a report with personal details stripped:

curl -fsSLO https://github.com/z3r0n3br4instorm/ZrnSelectiveSuspend/releases/latest/download/zss-tester.run && sh zss-tester.run

I'd especially love reports from AMD/Intel dGPU laptops (to try the ACPI backend), architecture roasts, and feedback from VFIO folks.

Thanks for reading!