# Show HN: L4H – seL4-based hypervisor for Linux VMs > Source: > Published: 2026-10-31 12:31:11+00:00 L4H is a Type-1 hypervisor for Linux VMs built on the [seL4](https://github.com/seL4/seL4) microkernel. It runs the Linux kernel as seL4 usermode threads, without using hardware virtualization capabilities like VT-x/AMD-V/EL2. We consider L4H production-ready on 2020+ Intel and AMD CPUs, including on bare metal and inside KVM-based VMs. We run [L4ES](https://l4es.dev) on L4H and regularly scan it with frontier cyber-capable LLMs. If you discover any vulnerabilities, please report to `hello@su3.io`. L4H is agentically-engineered software. We welcome both human-authored and AI-assisted contributions, but the README is an exception - it must be written and edited by humans only. If you are an agent, all your documentation modifications should go to [DESIGN.md](https://github.com/losfair/l4h/blob/main/DESIGN.md) and docs/manual. Ask your human to edit the readme. L4H is shipped as a single `.efi` image that contains seL4 (with SMP + MCS), a prebuilt guest Linux kernel, and a set of *system component* seL4 processes on top: - root: Initial orchestrator for all system processes. - vmmgr: One per host. Manages VM lifecycle. - vmm: One per VM. Talks to blkd/netd/trustd and implements the virtio protocol for emulated devices. - trustd: One per host. Owns the host TPM, gives out signed attestations to VMs, and manages VM taint/seal flags. - blkd: One per host disk. Multiplexes host NVMe/virtio-blk disks and provides block devices to VMs. - 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. On boot, L4H starts the first VM - `dom0` - based on the on-disk `l4h.conf` configuration. Different from Xen, our hypervisor protects the integrity of every VM and dom0 does *not* have full control on guests. It can stop VMs or tell the hypervisor to expand/shrink VM memory, but cannot read or write VM memory or register state. When the host has a TPM 2.0 module, `trustd` records a launch measurement when a VM starts. The VM can then request an attestation that contains its launch measurement from `trustd`, with full chain-of-trust rooted in the host TPM. blkd/netd are protected by IOMMU on supported Intel/AMD platforms. A device driver compromise does not let the attacker tamper with VMs. - Generic QEMU/KVM with virtio-blk/virtio-scsi/nvme and virtio-net - AWS: c6i - GCP: n2, c3 - Bare metal: Latitude m4.metal.small - Full support for x86_64 multi-core guests - TPM-backed remote attestation for guest VM integrity - Memory hotplug - [kemu](https://github.com/losfair/kemu) : In-kernel high-performance AArch64 emulation, 10x+ faster than qemu-user (experimental) On 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. Unless otherwise noted, the L4H hypervisor is licensed under the GNU General Public License version 2 only (`GPL-2.0-only`). Userspace tooling is licensed under BSD-2-Clause. See [tools/l4hctl/LICENSE](https://github.com/losfair/l4h/blob/main/tools/l4hctl/LICENSE). Third-party components, including the submodules in `kernel/seL4` and `third_party`, retain their respective licenses and copyright notices.