[xen] 18.04 dom0 on EFI fails to boot

[esbaixauli]

Hi!

I am trying to set up my laptop with Xen hypervisor to run other OSs as virtual machines.

I have managed to boot Xen EFI image (the one that comes with package xen-hypervisor-4.9-amd64) by modifying efibootmgr options and adding a new entry there. However, when trying to boot that entry, all I get is a blank screen that stays frozen for a few seconds and ends up with a white blinking cursor in the top left corner.

EDIT: First, it prints out how it load xen hypervisor, its config file, the Linux kernel and the initramfs, and two more lines with hex digits that I can't read because they disappear too fast. Then it goes blank.

What I have done is:

1. Install xen-hypervisor-4.9-amd64.
2. Create a new directory "xen" under /boot/efi/EFI with the following files:
   
   1. xen-4.9-amd.efi
   2. vmlinuz-4.15.0-45-generic
   3. initrd.img-4.15.0-45-generic
   4. xen.cfg, with the following content:
      

      [global]
      default=ubuntu
      
      [ubuntu]
      options=console=vga,com1 com1=115200,8n1 iommu=verbose ucode=scan flask=disabled conring_size=2097152  loglvl=all
      kernel=vmlinuz-4.15.0-45-generic root=UUID=24bd5658-bf88-41ae-85e7-11ea902a3c50= ro vt.handoff=7 console=hvc0
      ramdisk=initrd.img-4.15.0-45-generic

   
   
3. Added the new entry with the command efibootmgr -c -d /dev/nvme0n1 -L Xen -l "\EFI\xen\xen.efi"

All of this following the UEFI guide at Xen wiki: https://wiki.xenproject.org/wiki/Xen_EFI

My guess is that the config in xen.cfg is not adequate for booting Ubuntu. But the list of options (https://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html) is so long I have no idea how to write a proper config file.

Has anyone successfully booted Ubuntu 18.04 as dom0 on a UEFI machine (as I understand legacy boot does not require a cfg file)? Any ideas on what the cfg file should look like or what it lacks?

Thanks!!

[crimsonegret]

I have a working system under Ubuntu 18.04.02 by reading between the lines and not bothering to try to boot directly from EFI, but rather patch the grub.cfg generation that does _almost_ the right thing. If you look at the very bottom of the https://wiki.xenproject.org/wiki/Xen...n_as_gz_binary page, and ignore all the stuff about building grub from source or building a modified "grub2.efi," you will find a patch that you can adapt to use "multiboot2" and "module2" rather than the older versions to boot the xen kernel.

I believe this is all fixed in Grub 2.04, but Ubuntu (and upstream Debian) are not yet using that. Looks like Debian Testing (Bullseye) will have 2.04, so this will go away then, I would hope.