Abstract vGPU devices behind a framework dispatch

[yummybomb]

Summary

Bottom layer of the vendor VFIO vGPU stack (this ← #322 ← #363 ← #364 ← #321). Behavior-preserving refactor only — no lifecycle semantics change in this layer.

Kernel 6.8 hosts assign NVIDIA vGPUs through a vendor-specific VFIO interface instead of mdev, so the mdev-shaped seams get generalized before the new backend lands above:

• VGPUDevice / VGPUFramework abstraction — mdev moves behind a framework dispatch (CreateVGPU / DestroyVGPU / DiscoverVGPU), with assignments described by a framework + device path instead of a bare mdev UUID.
• Hypervisor wiring — QEMU receives the generalized vGPU path through VGPUDevicePath, while Cloud Hypervisor continues to receive the existing mdev path as a passthrough device.
• Metadata — VF allocation tracked with a single field; instance metadata carries GPUFramework / GPUDevicePath alongside the mdev UUID.
• QEMU args — vGPU attaches via sysfsdev, and the dead mdev branch is dropped from PCI passthrough args.

Testing

• go build ./..., go vet clean
• go test -race ./lib/devices/ ./lib/hypervisor/... and targeted lib/instances suites pass (TestSocketCacheKeyChangesWhenSocketIsRecreated and the network/image-dependent instances tests fail identically on the unmodified stack head in this environment)

---

Note

Medium Risk
Changes GPU attach/teardown and VM config paths across instance lifecycle and QEMU/CH, though Linux behavior still delegates to mdev; metadata migration relies on legacy UUID fallback.

Overview
Introduces a framework-agnostic vGPU layer (VGPUDevice, VGPUFramework, CreateVGPU / DestroyVGPU) so mdev is one backend today and future VFIO paths can plug in without threading mdev UUIDs through the stack.

Instance and hypervisor wiring now treat vGPU separately from whole-GPU PCI passthrough: metadata gains GPUFramework and GPUDevicePath (with legacy fallback from GPUMdevUUID), lifecycle create/start/stop/delete goes through releaseStoredVGPU, and hypervisor.VMConfig uses dedicated VGPUDevicePath for QEMU vfio-pci,sysfsdev=… and Cloud Hypervisor device passthrough. Preflight validation counts vGPU on its own so microvm slot limits stay correct.

Naming cleanup: SR-IOV VF occupancy is Allocated instead of HasMdev; resource reporting follows the same field.

^{Reviewed by Cursor Bugbot for commit 45c4460. Bugbot is set up for automated code reviews on this repo. Configure here.}

[sjmiller609]

• consider a struct param for DestroyVGPU(ctx, framework, devicePath, mdevUUID) — three positional strings are easy to swap silently as backends multiply
• error strings still say "create vGPU mdev for profile %s" — reword in whichever layer introduces non-mdev backends
• stop/delete log "uuid", stored.GPUMdevUUID — will be empty for path-only assignments; log the device path instead

[yummybomb]

addressed the review in 113d9e6 + 9396bc0:

• DestroyVGPU now takes a devices.VGPUAssignment struct instead of three positional strings — pulled the exact shape down from the next PR in the stack, so its diff collapses on restack
• stop/delete now log device_path (always populated) instead of the possibly-empty mdev uuid
• the "create vGPU mdev" error strings stay as-is in this layer since mdev is the only backend here; the layer that introduces the vendor backend already rewords them to "create vGPU for profile"

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit 28b9531. Configure here.}