UEFI and FreeBSD/Xen-12.1/4.12

[Roger Pau Monné]

On Sun, Nov 08, 2020 at 11:46:34PM -0800, Brian Buhrow wrote:
> 	hello.  I'm trying to get an installation of FreeBSD-12.1 / xen 4.12
> running an Intel DQ67SW motherboard with 4 8TB disks attached to it up and
> running.   Everything seems to work fine, except that the BIOS will not
> boot from the hard drives in legacy mode on its own.  If I manually select
> a disk from the boot menu, FreeBSD and Xen load  as they should.  The Intel
> site says that booting from disks larger than 2TB is only supported if UEFI
> booting is enabled.  It's my understanding that Freebsd-Xen will not run
> if one doesn't boot in legacy mode.
> 	Any suggestions on how to work around this conflict?  Is it now
> possible to boot FreeBSD as Dom0 in UEFI boot mode?

In order to boot FreeBSD/Xen dom0 using UEFI we need to add support
for the multiboot2 [0] boot protocol, so that the FreeBSD loader can do
the handoff to the Xen kernel. We currently only have multiboot1
implemented in the FreeBSD loader, and hence we are limited to legacy
(BIOS) boot.

I've been meaning to fix this and add support for multiboot2, but so
far I haven't got the time to actually do the work. If someone is
interested in working on this I'm happy to help, but it does require
someone that's slightly familiar with the loader.

Roger.

[0] https://www.gnu.org/software/grub/manual/multiboot2/multiboot.html