Booting Xen
===========

Xen follows the zImage protocol defined for 32-bit ARM Linux[1] and the
Image protocol defined for ARM64 Linux[2].

In both cases the recommendation to boot in HYP/EL2 mode is a strict
requirement for Xen.

The exceptions to this on 32-bit ARM are as follows:

 Xen does not require the machine type to be passed in r1. This
 register is ignored (so may be invalid or the actual machine type).

 Xen does not support the ATAG list and requires Device
 Tree. Therefore r2 must point to the physical address of device tree
 block (dtb) in system RAM.

 NOTE: although Xen uses the zImage protocol there is no compression
 actually used. This should be transparent to the bootloader. The
 zImage protocol should still be used and not the stricter "raw
 (non-zImage)" protocol described in arm/Booting.

There are no exception on 64-bit ARM.


Firmware/bootloader requirements
--------------------------------

Xen relies on some settings the firmware has to configure in EL3 before starting Xen.

* Xen must be entered in NS EL2 mode

* The bit SCR_EL3.HCE (resp. SCR.HCE for 32-bit ARM) must be set to 1.


[1] linux/Documentation/arm/booting.rst
Latest version: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm/booting.rst

[2] linux/Documentation/arm64/booting.rst
Latest version: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm64/booting.rst
