QEMU Guest Kernel

Linux kernel configurations for QEMU/KVM guests, statically linked for direct kernel boot.

Architectures

i686: x86, i686 w/o PAE.
- Choose x86-64 kernel if RAM > 3 GiB.
x86_64: x86, generic x86-64.

How to build

Native build

ARCH=<see_below>

wget url://to/linux-5.10.<y>.tar.xz
tar xf linux-5.10.<y>.tar.xz
cp {filesystem,systemd}.config arch_$ARCH.config linux-5.10.<y>/kernel/configs/
cd linux-5.10.<y>/

make defconfig
make kvm_guest.config
make filesystem.config
make systemd.config
make arch_$ARCH.config
make -j<N>

Cross build

Install Clang/LLVM toolchain, then

export ARCH=<see_below>
export CROSS_COMPILE=<see_below>
export LLVM=1

wget url://to/linux-5.10.<y>.tar.xz
tar xf linux-5.10.<y>.tar.xz
cp {filesystem,systemd}.config arch_$ARCH.config linux-5.10.<y>/kernel/configs/
cd linux-5.10.<y>/

make <see_below>defconfig
make kvm_guest.config
make filesystem.config
make systemd.config
make arch_$ARCH.config
make -j<N>

Architecture	Kernel `ARCH`	`CROSS_COMPILE`	`defconfig` prefix
`i686`	`x86`	`i686-linux-gnu-`	`i386`
`x86_64`	`x86`	`x86_64-linux-gnu-`	`x86_64`

How to use

QEMU command line:

qemu-system-<arch> -kernel /path/to/bzImage -append "root=/dev/vdXY rootfstype=<fstype> rootflags=<mountflags> rw" ...

Libvirt XML:

<domain type="kvm">
  <!-- ... -->
  <os>
    <!-- ... -->
    <kernel>/path/to/bzImage</kernel>
    <cmdline>root=/dev/vdXY rootfstype=[fstype] rootflags=[mountflags] rw</cmdline>
  </os>
</domain>

Virt-manager GUI:
- Switch to “Details” tab,
- In “Boot options”, expand “Direct kernel boot” block,
- Check “Enable direct kernel boot”,
- Set “Kernel path” and “Kernel args”, “Initrd path” can be safely omitted.

AppArmor

The Linux kernel use SELinux as security module by default. To use AppArmor instead, set either lsm=apparmor or selinux=0 security=apparmor in kernel command line args.

IMCG / qemu