Linux and KVM on the Odroid-C4

CellulOS has two VMM implementations, and a natural question is how they compare against a real hypervisor on the same silicon. That means running Linux with KVM on the Odroid-C4.

You cannot do this with HardKernel’s stock image. This page explains why — there are two independent blockers, and the second one is subtle enough that fixing only the first leaves you stuck — and gives the rebuild that works.

Why the stock image cannot run KVM

Blocker 1: CONFIG_KVM is off. HardKernel’s Ubuntu 22.04 image ships a Linux 4.9 BSP kernel with CONFIG_KVM disabled. There is no /dev/kvm. This is true even though the CPUs do start at EL2, so the hardware is perfectly capable — it is purely a kernel config decision.

Blocker 2: the device tree hides half the GIC. This is the one that will waste your afternoon. Even after you turn CONFIG_KVM on, the vendor kernel still cannot run KVM, because its device tree declares only GICD and a truncated GICC — it omits GICH (hypervisor control) and GICV (virtual CPU interface) entirely.

KVM’s vGICv2 needs all four regions. Without GICH and GICV in the DT it has no way to inject virtual interrupts, so it refuses to initialise regardless of the config flag.

The fix

Rebuild the vendor kernel with KVM enabled and a corrected GIC node.

1. Get the source

git clone --depth 1 --branch odroidg12-4.9.y https://github.com/hardkernel/linux.git
# 4.9.337

2. Enable KVM

CONFIG_KVM=y
CONFIG_KVM_ARM_HOST=y

3. Patch the device tree

In arch/arm64/boot/dts/amlogic/mesonsm1.dtsi, the gic node must claim arm,gic-400 and declare all four regions:

Region	Base	Size
GICD (distributor)	0xffc01000	0x1000
GICC (CPU interface)	0xffc02000	0x2000
GICH (hypervisor control)	0xffc04000	0x2000
GICV (virtual CPU interface)	0xffc06000	0x2000

Note that GICC is also widened from 0x0100 to 0x2000, matching mainline meson-g12-common.dtsi. The resulting node:

gic: interrupt-controller@2c001000 {
        compatible = "arm,gic-400", "arm,cortex-a15-gic", "arm,cortex-a9-gic";
        ...
        reg = <0x0 0xffc01000 0 0x1000>,   /* GICD */
              <0x0 0xffc02000 0 0x2000>,   /* GICC */
              <0x0 0xffc04000 0 0x2000>,   /* GICH */
              <0x0 0xffc06000 0 0x2000>;   /* GICV */
};

The patch is saved in the OSmosis repo at scripts/odroid-c4-bench/odroid-c4-kvm-gic.patch.

4. Cross-compile with gcc-11

Attention

Use gcc-11. A 4.9 kernel tree is far too old for gcc-13 and the build will fail with errors that have nothing to do with anything you changed.

make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CC=aarch64-linux-gnu-gcc-11 -j$(nproc) Image.gz dtbs

5. Install

Copy the resulting Image.gz and the patched dtb into the board’s FAT boot partition, mounted at /media/boot.

Attention

Back up the originals first. /media/boot holds the only copy on the card, and a bad kernel there means re-flashing the SD.

6. Confirm it worked

On the next boot, dmesg should show:

kvm: Hyp mode initialized successfully
kvm: vgic-v2@ffc04000

and /dev/kvm should exist. The vgic-v2@ffc04000 line is the direct payoff from the DT patch — that address is GICH, which the stock tree never declared.

Board Linux practicalities

Small things, each of which cost us time:

• Login is root / odroid.

• There is no DHCP on the wired link — the host side is a static 10.42.0.1/24 (see Host Setup). Give the board a static 10.42.0.2/24 and persist it with systemd-networkd:

  # /etc/systemd/network/10-wired.network
  [Match]
  Name=eth0
  
  [Network]
  Address=10.42.0.2/24
  Gateway=10.42.0.1
  

  systemctl enable --now systemd-networkd
  

• The C4 has no RTC. Its clock is years off after every power cycle, and apt consequently rejects the repository release files (“Release file is not yet valid”). Set the date before touching apt:

  date -s "2026-07-11 12:00:00"     # or use timedatectl/NTP once networking is up
  

• Before networking exists, drive the board over the serial console with scripts/odroid-c4-bench/serial_shell.py, which handles the login prompt and returns command output.