Build An Accelerated KVM Guest Custom Kernel for WSL 2

build-accelerated-kvm-guest-custom-kernel-for-wsl2.md

I'm not the author the blog post and this gist is a simply a note on my usage based on the original post, https://boxofcables.dev/kvm-optimized-custom-kernel-wsl2-2022/.

I also changed the code that extract the latest to a concrete linux kernel version.

First start with openSUSE Tumbleweed distro and commands below can be used to build the custom kernel and set it to be used for WSL2 distros.

# prepare build deps
sudo zypper -n up
# original from the post
sudo bash -c "zypper in -y -t pattern devel_basis && zypper in -y bc openssl openssl-devel dwarves rpm-build libelf-devel aria2 jq"
# what I ended up doing instead
sudo zypper install -y aria2 make gcc bison flex bc libelf-devel libopenssl-3-devel dwarves

# download and unpack kernel source code and cd into it
echo 'https://github.com/microsoft/WSL2-Linux-Kernel/archive/refs/tags/linux-msft-wsl-6.1.21.1.tar.gz' | aria2c -i -
tar -xf *.tar.gz
cd WSL2-Linux-Kernel-linux-msft-wsl-6.1.21.1/

# modify config
cp Microsoft/config-wsl .config
sed -i 's/# CONFIG_KVM_GUEST is not set/CONFIG_KVM_GUEST=y/g' .config
sed -i 's/# CONFIG_ARCH_CPUIDLE_HALTPOLL is not set/CONFIG_ARCH_CPUIDLE_HALTPOLL=y/g' .config
sed -i 's/# CONFIG_HYPERV_IOMMU is not set/CONFIG_HYPERV_IOMMU=y/g' .config
sed -i '/^# CONFIG_PARAVIRT_TIME_ACCOUNTING is not set/a CONFIG_PARAVIRT_CLOCK=y' .config
sed -i '/^# CONFIG_CPU_IDLE_GOV_TEO is not set/a CONFIG_CPU_IDLE_GOV_HALTPOLL=y' .config
sed -i '/^CONFIG_CPU_IDLE_GOV_HALTPOLL=y/a CONFIG_HALTPOLL_CPUIDLE=y' .config
sed -i 's/CONFIG_HAVE_ARCH_KCSAN=y/CONFIG_HAVE_ARCH_KCSAN=n/g' .config
sed -i '/^CONFIG_HAVE_ARCH_KCSAN=n/a CONFIG_KCSAN=n' .config

# build kernel
make -j 8

# move kernel to Windows host
powershell.exe /C 'Copy-Item .\arch\x86\boot\bzImage $env:USERPROFILE'
# print '$env:USERPROFILE\.wslconfig' just in case it existed before
cat /mnt/c/Users/$(powershell.exe '$env:USERNAME')/.wslconfig
# set kernel file path to '$env:USERPROFILE\.wslconfig'
powershell.exe /C 'Write-Output [wsl2]`nkernel=$env:USERPROFILE\bzImage | % {$_.replace("\","\\")} | Out-File $env:USERPROFILE\.wslconfig -encoding ASCII'
# verify the content
cat /mnt/c/Users/$(powershell.exe '$env:USERNAME')/.wslconfig

And now this built kernel be the kernel for all wsl distros not just for openSUSE one unless the setting gets reversed later.

My other notes on Windows