How to control booting via BIOS vs booting via EFI?

[Johan Stenstam <johani%johani.org@localhost>]

Hi,

I have an Minisforum MS-01 which I like a lot. In fact I like it so much that I bought a second one. The first one runs NetBSD 10.1/Xen and the second one should do that too, but doesn’t. 

The problem seems to be that when I load the Xen hypervisor (i.e. from boot.cfg, multiboot…) on the second system it crashes. Same version of Xen on both systems. After some hunting around I’ve become aware that apparently NetBSD/Xen must boot via BIOS, EFI doesn’t work at the moment. So I checked “sysctl machdep.bootmethod” and as the first box says “BIOS” and the second says “EFI” I believe that I have found the problem.

So I tried to switch the second system to do BIOS-booting instead (I don’t know why it chosed EFI, I do not remember being given a choice). No luck, no matter how much I play with installboot and copying /usr/mdec/boot to /boot and similar stuff from the BIOS era, system always boots via EFI. Sigh.

Here it is worth pointing out that neither system announces any BIOS/Legacy-booting ability. Also they have slightly different versions of the Minisforum firmware (1.26 vs 1.27). So perhaps 1.26 didn’t announce the BIOS-booting ability but did support it, while 1.27 actually removed BIOS-booting? That would suck as I really need to be able to run Xen.

To test this I switched the disks between the two systems. And then, suddenly, the older MS-01 only does EFI-booting while the newer only does BIOS-booting. That’s actually great, because it means that both systems are *able* to boot via BIOS, which I need for Xen.

Which brings me to my current conundrum: as the BIOS vs EFI-booting apparently follows the disk used it must be something on the disk that determines the boot method. But what? And how do I change it? Both disks use GPT, have identical GPT tables from start until the NetBSD partitions (although the new disk is larger). Output from “fdisk /dev/rld0” is identical. Contents of the “PBR” is the same, /boot is the same, etc, etc.

I simply do not understand where on the disk the magic lies that determine boot method.

Any help would be much appreciated.