Xen ARM with Virtualization Extensions

For the ARM port supporting paravirtualized guests on processors without the virtualization extensions see Xen ARM (PV).

The ARM v7-A architecture includes the optional virtualization extensions that allow a hypervisor to manage fully hardware virtualized guests. These extensions will be available in some ARM Cortex A15 and Cortex A7 processors.

Status

This port is a work-in-progress and cannot yet start any guests (other than dom0).

Guest ABI

The guest (including dom0) visible ABI exposed by the hypervisor is not yet set in stone and there may be changes as work progresses. See requirements (below) for specific details of matching kernel and hypervisor versions.

Contributing

Please email xen-devel with comments, questions and patches. Please see the list info page for subscription information and the archives. For patches please see Submitting Xen Patches.

The xen-arm mailing list is focussed on Xen ARM (PV) port.

Hardware

Currently there are no processors available which implement the virtualisation extensions. Therefore we are currently targetting the Real-time System Model's provided by ARM. See Xen ARMv7 with Virtualization Extensions/FastModels for more information on obtaining and building the necessary model.

Requirements

ARM Fast Model

Either the v7-A ARM Envelope Model (AEM) or the Cortex A15/A7 models (single CPU only).

Device Tree

A device tree in the flat device tree format (.dtb). The device tree source for the AEM is here: git://xenbits.xen.org/people/dvrabel/device-trees.git.

Xen

While xen-unstable is frozen for the 4.2 release ARM patches are being collected in the arm-for-4.3 branch of this git tree. This tree is based upon Anthony Perards conversion to git.

Linux kernel for dom0

3.5-rc7-arm-2 branch of [1]

dom0 userspace

(more details here)

Hypervisor

ABI Compatibility

Xen commit 25024:b8a5e8100c5d and later requires at least commit ef9437e20b9e549282a4602f1187023e4ad2c697 from dvrabel/linux.git#vexpress-dt. Older hypervisors require a Linux version before that (i.e. you must have either both patches or neither).

Device Trees

Xen needs the device trees to be in the flat device tree format (the device tree blob or DTB). This is built by the device tree compiler (dtc) from the device tree source files (.dts and .dtsi.

Version 1.3 or later of dtc is required.

Build the .dtb files with make.

A pre-built vexpress-v2p-aem-v7a.dtb.

Xen

When running on the model there is no bootloader to provide the DTB. Instead, it is linked with the xen image.

The DTB to use is specified by the CONFIG_DTB_FILE config variable which should be set to the absolute path of the DTB. This variable may be set in .config or on the make command line.

The Xen command line may be set with the bootargs parameter of the chosen node of the device tree.

Dom0 kernel

Enable at least ARCH_VEXPRESS, ARCH_VEXPRESS_DT. Disable SPARSE_IRQ (it doesn't play nicely with device tree support). If ARM_APPENDED_DTB is enabled then any appended DTB will be used instead of one supplied by Xen and the kernel will crash unless the memory in the DTB matches that location/size supplied by Xen.

A working configuration is available here.

The Linux command line should be set with the xen,dom0-bootargs parameter of the chosen node of the device tree supplied to Xen. If this parameter is missing then Linux will not get a command line and the wrong console will be used (there's a bug where the kernel doesn't use the default, built-in command line if the /chosen node is missing.

Flash Image

The dom0 kernel is loaded by Xen from the beginning of the flash.

Native boot

To boot the kernel natively use an updated boot-wrapper from git://xenbits.xen.org/people/dvrabel/boot-wrapper.git.

Build the device tree blobs provided with the kernel with make dtbs. A suitable DTB file for the envelope model is vexpress-v2p-aem-v7a.dtb.

For a native boot the kernel should have ARM_APPENDED_DTB and ARM_ATAG_DTB_COMPAT enabled. The kernel zImage and the DTB should be appended. e.g., cat zImage vexpress-v2p-aem-v7a.dtb > image.bin.

Developer FAQs

Use the Xen ARMv7 Dev FAQ page to cover commonly asked questions.