Tuesday, November 26, 2013

KVM on ARM Cortex A15 (OMAP5432 UEVM)

Hi! In this post I'll summarize the steps I needed to do in order to get KVM working on the OMAP5 ARM board using the virtualization extensions.

ARM A15 HYP mode.

In Cortex-A15, ARM have introduced a new operating mode called HYP (hypervisor). It has lower permissions than TruztZone. In fact, HYP splits the "insecure" world into two parts, one for hypervisor and the other one for the guests. By default on most boards the system boots into the insecure non-HYP mode. To enter the HYP mode, one needs to use platform-specific ways. For OMAP5 this involves making a call to the TrustZone which will restart the insecure mode cores.

A good overview of how virtualization support for ARM was added to Linux is available at LWN.

Ingo Molnar HYP patch

There was a patch for u-boot to enable entering HYP mode on OMAP5 by Ingo Molnar. Too bad, it was either written for an early revision of omap5 or poorly tested. It did not work for my board, so I had to learn about OMAP5 TrustZone SCM commands from various sources and put up a patch (which is integrated to my u-boot branch).
If you're interested, you can take a look at the corresponding mailing list entry.


Preparing u-boot SD card

Get the android images from TI or build them yourself. You can use the usbboot tool to boot images from the PC. Or even better, you can build u-boot (this is the preferred way) and then you won't need android images. But you may need the TI GLSDK for the x-loader (MLO). Creating an SD card with u-boot is the same as for omap3 and omap4, so I'll leave this out. There is some magic with creating a proper partition table, so I advise that you get some prebuilt image (like ubuntu for pandaboard) and then replace the files in the FAT partition.


Please consult the OMAP5432 manual on how to set up the DIP switches to boot from SD card.

Source code

For u-boot:

For linux kernel:

Linux kernel is based on the TI omapzoom 3.8-y branch. I fixed a null pointer in the DWC USB3 driver and some issues with the 64-bit DMA bitmasks (I hacked the drivers to work with ARM LPAE, but this probably broke them for anything else. The upstream has not yet decided on how this should be handled).

Compiling stuff

First, let's build the u-boot
export PATH=/home/alexander/handhelds/armv6/codesourcery/bin:$PATH
export ARCH=arm
export CROSS_COMPILE=arm-none-eabi-
make clean
make distclean
make ${U_BOARD}_config
make -j8

you'll get the u-boot.bin and the u-boot.img (which can be put to the SD card). Besides, that will build the mkimage tool that we'll need later.

Now, we need to create the boot script for u-boot that will load the kernel and the device tree file to RAM.

i2c mw 0x48 0xd9 0x15
i2c mw 0x48 0xd4 0x05
setenv fdt_high 0xffffffff
fdt addr 0x80F80000
mmc rescan
mmc part
fatload mmc 0:1 0x80300000 uImage
fatload mmc 0:1 ${fdtaddr} omap5-uevm.dtb
setenv mmcargs setenv bootargs console=ttyO2,115200n8 root=/dev/sda1 rw rootdelay=5 earlyprintk nosmp
run mmcargs
bootm 0x80300000 - ${fdtaddr} 

Now, compile it to the u-boot binary format:
./tools/mkimage -A arm -T script -C none -n "omap5 boot.scr" -d boot.txt boot.scr

Building linux:

export PATH=/home/alexander/handhelds/armv6/linaro-2012q2/bin:$PATH
export ARCH=arm
export CROSS_COMPILE=/home/alexander/handhelds/armv6/linaro-2012q2/bin/arm-none-eabi-
export OMAP_ROOT=/home/alexander/handhelds/omap

pushd .
cd ${OMAP_ROOT}/kernel_omapzoom
make $MAKE_OPTS omap5uevm_defconfig
make $MAKE_OPTS zImage

Now, we need to compile the DTS (device tree source code) using the dtc tool. If you choose to use the usbboot instead of u-boot, you can enable the config option in kernel and simply append the DTB blob to the end of zImage.
(Boot Options -> Use appended device tree blob to zImage)

./scripts/dtc/dtc arch/arm/boot/dts/omap5-uevm.dts -o omap5-uevm.dtb -O dtb
cat kernel_omapzoom/arch/arm/boot/zImage omap5-uevm.dtb > kernel
./usbboot -f; fastboot -c "console=ttyO2 console=tty0 rootwait root=/dev/sda1" -b 0x83000000 boot kernel


For userspace part, I've followed the manual from VirtualOpenSystems for versatile express. The only tricky part was building qemu for the ArchLinux ARM host, and the guest binaries are available for download.

P.S. please share your stories on how you're using or plan to use virtualization on ARM