Xen on Raspberry Pi 4

[Paul Leiber <paul@xxxxxxxxxxxxxxxx>]

Hi list,

Now that the devices are available again, I got hold of a Raspberry Pi 4 
(8 GB) which I am currently trying to set up Xen on for using it as a 
backup server.
What I did was to install a standard Debian distribution booted via 
EFI/GRUB2 (following 
https://forums.raspberrypi.com/viewtopic.php?t=282839) and then install 
the xen-System-arm64 package via apt. I have output on a console via 
UART (at least when booting Debian without Xen, see hypothesis 3 below).
Booting Debian without Xen is working fine. (Although I only see the 
Grub selection menu via UART when no HDMI is plugged in while booting.)
Selecting Xen in Grub leads to the following output on the console right 
after Grub hands over:
Loading Xen 4.17-arm64.efi ...
Loading Linux 6.1.0-10-arm64 ...
Loading initial ramdisk ...
Using modules provided by bootloader in FDT
Xen 4.17.2-pre (c/s ) EFI loader

And then the output stops.

I have four hypotheses (not mutually exclusive, and there are very 
probably unknown unknowns on my side):
1. Booting Xen via EFI is not working, and I need to use U-Boot as 
described in 
https://xenproject.org/2020/09/29/xen-on-raspberry-pi-4-adventures/
2. The Debian package xen-system-arm64 is not suitable for this purpose 
and I need to compile Xen from scratch
3. I got the console settings wrong (I currently use the settings from 
https://xenproject.org/2020/09/29/xen-on-raspberry-pi-4-adventures/ for 
Xen command line specified in Grub, but I also tried a lot of different 
settings), and Xen is actually doing something, but I don't see the output.
4. There is something wrong with my setup and I need to change specific 
EFI and/or other settings.
Has anybody got a similar setup working and can give me hints?

I am aware of https://github.com/dornerworks/xen-rpi4-builder, I might 
try this as one of the next steps, but I'd rather stick with Debian, if 
possible.
Thanks,

Paul