KVM virtualization on ARM Chromebook laptop

Requirements

The basic requirements of this guide are:

Samsung's ARM Chromebook laptop

USB flash disk, SD or microSD (with adapter) card (4 GB or more recommended)

Personal computer with Ubuntu 13.04 or similar distribution

The ARM Chromebook

Booting from USB or SD

By default, even in Developer Mode, booting from external media is disabled. We will first have to boot into Chrome OS to enable USB or SD/microSD booting.

From a powered-off state:

Press the power key, then Ctrl-D in the OS verification screen.

When the system is in the login screen, press Ctrl-Alt + ->, which is Control + Alt + Forward key (forward key is located right next to the refresh key).

In the console terminal login with the account root (no password should be asked)

Type crossystem dev_boot_usb=1

Now every time we reboot, we can boot from an external source (USB or SD), by pressing Ctrl-U.

Cross compiler and required packages

To complete the next steps we need to install a cross compiler, and a couple of required packages on our workstation's distribution (Ubuntu 13.04):

$ sudo apt-get install build-essential git u-boot-tools qemu-user-static gdisk cgpt \
                       libncurses5-dev flex bison vboot-kernel-utils debootstrap

And for the cross compiler:

$ sudo apt-get install gcc-arm-linux-gnueabihf

Compiling the host and guest Linux kernel

Pre-compiled kernel images and DTB files can be downloaded from our site:

$ wget http://www.virtualopensystems.com/downloads/guides/kvm_on_chromebook/uImage
$ wget http://www.virtualopensystems.com/downloads/guides/kvm_on_chromebook/guest_zImage
$ wget http://www.virtualopensystems.com/downloads/guides/kvm_on_chromebook/exynos5250-snow.dtb
$ wget http://www.virtualopensystems.com/downloads/guides/kvm_on_chromebook/rtsm_ve-cortex_a15x1.dtb

For Chromebook we use as a base version the mainline 3.13 branch which also includes KVM on ARM support. To download the kernel from the Virtual Open Systems repository, follow these steps:

$ git clone git://github.com/virtualopensystems/linux-kvm-arm.git
$ cd linux-kvm-arm
$ git checkout origin/chromebook-3.13 -b chromebook-3.13

For the kernel configuration specific to the laptop run:

$ curl http://www.virtualopensystems.com/downloads/guides/kvm_on_chromebook/config > .config

We can now proceed with compiling the actual kernel:

$ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make uImage dtbs -j4

Copy arch/arm/boot/uImage and arch/arm/boot/dts/exynos5250-snow.dtb in a location that you can find later, as now we can proceed with compiling the guest kernel

The guests that we will create later will be based on the Versatile Express QEMU machine model. For we will use a different kernel branch specific to that platform:

$ git checkout origin/kvm-vexpress-3.9
$ curl http://www.virtualopensystems.com/downloads/guides/kvm_on_chromebook/guest-config > .config
$ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make zImage dtbs -j4

Then we can append the dtb file to the kernel image with:

$ cat arch/arm/boot/dts/rtsm_ve-cortex_a15x1.dtb >> arch/arm/boot/zImage

That way we only need to handle one file. Make sure to copy arch/arm/boot/zImage for later usage.

Bootloader

If you wish to skip this chapter you can download a pre-compiled binary of the bootloader:

$ wget http://www.virtualopensystems.com/downloads/guides/kvm_on_chromebook/nv_u-boot-snow.kpart

To be able to run KVM on ARM platforms, the kernel has to be booted in hypervisor mode. Because of this relatively recent requirement (due to the introduction of the virtualization extensions), up until now all booting methods would boot the kernel in the standard Supervisor mode.

For the ARM Chromebook the default boot procedure doesn't allow us to boot in hypervisor mode. Although the laptop's boot mechanism is based on the frequently used u-boot, the binary is located in RO memory. Fortunately, a chained u-boot mechanism can be used (i.e. starting another u-boot after the original). We can then enter hypervisor mode from the our custom iteration of u-boot and subsequently load our kernel and userspace.

Checkout the needed u-boot code:

$ git clone git://github.com/virtualopensystems/u-boot.git
$ cd u-boot
$ ./scripts/build.sh

If successful, a message about how to copy the bootloader on the USB flash disk or SD card will appear. We will use it later when preparing the boot medium to start our system. If you have followed the Setting up the boot medium chapter and you have a prepared boot device, then you can update u-boot by running:

$ sudo dd if=nv_uboot-snow.kpart of=/dev/sdX1

Wireless networking

To setup the wireless network on the host, we'll need wpasupplicant.

$ sudo chroot ./precise
$ apt-get install wpasupplicant
$ exit

Next, get the WiFi card firmware and extract it to in precise folder:

$ wget http://www.virtualopensystems.com/downloads/guides/kvm_on_chromebook/firmware_mrvl.xz
$ sudo tar xvf firmware_mrvl.xz -C precise/

wpasupplicant will need a configuration file. To generate one automatically run the following command and save its output to /etc/wpa_supplicant.conf. For more options look man wpa_supplicant.conf:

wpa_passphrase "You Network's SSID HERE"

The command will then ask for the Network's password and will output the contents of /etc/wpa_supplicant.conf:

network={
   ssid="MyWPAWiFI"
   #psk="YourPassword"
   psk=PasswordString
}

Optionally you can be more verbose by adding the following fields on the configuration file depending on your wireless setup:

scan_ssid=1 (if the SSID is hidden)
proto=WPA
key_mgmt=WPA-PSK

Tweak etc/network/interfaces to enable WiFi networking (erroneous settings will extend boot up time):

auto lo
iface lo inet loopback

dns-nameservers 8.8.8.8
auto mlan0
iface mlan0 inet dhcp
wpa-driver nl80211
wpa-conf /etc/wpa_supplicant.conf

Note that in case the wireless network does not work, your boot time might be extended to around 2 minutes, trying to bring mlan0 up. Alternatively, edit /etc/init/failsafe.conf and comment out the sleep commands to make the boot process faster.

In case you need to try an alternate configuration you can always restart the service by issuing the following commands:

$ service network-interface restart INTERFACE=mlan0

or

$ ifdown mlan0
$ ifup mlan0

The userspace is now ready, we will later use the files created from this step on both the host (the Chromebook) and the guest.

Android userland creation

For the Android filesystem download the pre-built image:

$ wget http://www.virtualopensystems.com/downloads/guides/kvm_android_on_fastmodels/jb_ve_4_1_1.bz2

Then, create an image file and format it as an ext3 filesystem:

$ dd if=/dev/zero of=./android.img bs=1MiB count=512
$ mkfs.ext3 ./android.img

Finally, mount the image file and extract the userland files in it:

$ mkdir mnt
$ sudo mount -o loop android.img mnt
$ sudo tar xpjvf jb_ve_4_1_1.bz2 -C mnt/ --numeric-owner
$ sudo umount mnt