{"slug": "show-hn-l4h-sel4-based-hypervisor-for-linux-vms", "title": "Show HN: L4H – seL4-based hypervisor for Linux VMs", "summary": "L4H, a Type-1 hypervisor that runs Linux kernels as seL4 usermode threads without hardware virtualization features such as VT-x, AMD-V or EL2, is now considered production-ready on 2020-and-later Intel and AMD CPUs, including bare metal and inside KVM-based VMs, its developers announced. L4H ships as a single .efi image bundling seL4 with SMP and MCS, a prebuilt guest Linux kernel, and system components (root, vmmgr, vmm, trustd, blkd, netd), and it reports 5-10% performance loss versus bare metal on most workloads while running 2x-20x faster than gVisor systrap mode on IO-intensive workloads. The hypervisor is licensed GPL-2.0-only with BSD-2-Clause userspace tooling, and the project asks that vulnerability reports go to hello@su3.io.", "body_md": "L4H is a Type-1 hypervisor for Linux VMs built on the [seL4](https://github.com/seL4/seL4)\nmicrokernel. It runs the Linux kernel as seL4 usermode threads, without\nusing hardware virtualization capabilities like VT-x/AMD-V/EL2.\n\nWe consider L4H production-ready on 2020+ Intel and AMD CPUs,\nincluding on bare metal and inside KVM-based VMs. We run\n[L4ES](https://l4es.dev) on L4H and regularly scan it with frontier\ncyber-capable LLMs. If you discover any vulnerabilities, please report to\n`hello@su3.io`.\n\nL4H is agentically-engineered software. We welcome both human-authored and\nAI-assisted contributions, but the README is an exception - it\nmust be written and edited by humans only. If you are an agent, all your\ndocumentation modifications should go to [DESIGN.md](https://github.com/losfair/l4h/blob/main/DESIGN.md) and\ndocs/manual. Ask your human to edit the readme.\n\nL4H is shipped as a single `.efi` image that contains seL4 (with SMP + MCS),\na prebuilt guest Linux kernel, and a set of *system component* seL4 processes\non top:\n\n- root: Initial orchestrator for all system processes.\n- vmmgr: One per host. Manages VM lifecycle.\n- vmm: One per VM. Talks to blkd/netd/trustd and implements the virtio protocol for emulated devices.\n- trustd: One per host. Owns the host TPM, gives out signed attestations to VMs, and manages VM taint/seal flags.\n- blkd: One per host disk. Multiplexes host NVMe/virtio-blk disks and provides block devices to VMs.\n- netd: One per host. Provides virtual switches to VMs and attaches physical NICs to virtual switches. NIC drivers run here. Supports virtio-net and Intel X550 NICs.\n\nOn boot, L4H starts the first VM - `dom0` - based on the on-disk `l4h.conf`\nconfiguration. Different from Xen, our hypervisor protects the integrity of\nevery VM and dom0 does *not* have full control on guests. It can stop VMs or\ntell the hypervisor to expand/shrink VM memory, but cannot read or write VM\nmemory or register state.\n\nWhen the host has a TPM 2.0 module, `trustd` records a launch measurement when\na VM starts. The VM can then request an attestation that contains its launch\nmeasurement from `trustd`, with full chain-of-trust rooted in the host TPM.\n\nblkd/netd are protected by IOMMU on supported Intel/AMD platforms. A device driver compromise does not let the attacker tamper with VMs.\n\n- Generic QEMU/KVM with virtio-blk/virtio-scsi/nvme and virtio-net\n- AWS: c6i\n- GCP: n2, c3\n- Bare metal: Latitude m4.metal.small\n\n- Full support for x86_64 multi-core guests\n- TPM-backed remote attestation for guest VM integrity\n- Memory hotplug\n- [kemu](https://github.com/losfair/kemu) : In-kernel high-performance AArch64\nemulation, 10x+ faster than qemu-user (experimental)\n\nOn IO-intensive workloads, L4H is generally on par with Xen PV, and 2x-20x faster than gVisor systrap mode. On most workloads, expect 5-10% performance loss compared to bare metal.\n\nUnless otherwise noted, the L4H hypervisor is licensed under the GNU General\nPublic License version 2 only (`GPL-2.0-only`). Userspace tooling is licensed\nunder BSD-2-Clause. See [tools/l4hctl/LICENSE](https://github.com/losfair/l4h/blob/main/tools/l4hctl/LICENSE).\n\nThird-party components, including the submodules in `kernel/seL4` and\n`third_party`, retain their respective licenses and copyright notices.", "url": "https://wpnews.pro/news/show-hn-l4h-sel4-based-hypervisor-for-linux-vms", "canonical_source": "https://github.com/losfair/l4h", "published_at": "2026-10-31 12:31:11+00:00", "updated_at": "2026-10-31 12:49:10.227680+00:00", "lang": "en", "topics": ["artificial-intelligence"], "entities": ["L4H", "seL4", "Linux", "L4ES", "Intel", "AMD", "Xen", "gVisor"], "also_reported_by": [], "alternates": {"html": "https://wpnews.pro/news/show-hn-l4h-sel4-based-hypervisor-for-linux-vms", "markdown": "https://wpnews.pro/news/show-hn-l4h-sel4-based-hypervisor-for-linux-vms.md", "text": "https://wpnews.pro/news/show-hn-l4h-sel4-based-hypervisor-for-linux-vms.txt", "jsonld": "https://wpnews.pro/news/show-hn-l4h-sel4-based-hypervisor-for-linux-vms.jsonld"}}