#1000496 upgrade-reports: libvirt/kvm/qemu/grub - XML-generated VMs working under buster fail with bullseye

Package:
grub2
Source:
grub2
Description:
GRand Unified Bootloader, version 2 (dummy package)
Submitter:
amodia
Date:
2021-12-23 20:15:03 UTC
Severity:
grave
Tags:
#1000496#5
Date:
2021-11-24 08:28:39 UTC
From:
To:
Dear Maintainer,

after the upgrade from buster to bullseye virtual machines generated
with libvirt do not start.
Expected outcome was that all VMs start as usual (under buster).

Introspecting the boot progress with virt-viewer shows that
- GRUB hangs in rescue mode
- GRUB complains about a missing disk (identified by UUID)
- GRUB only lists one HD ('ls (hd0)') WITHOUT its partitions.

Definition of HDs in the XML file:
   <devices>
     <emulator>/usr/bin/kvm</emulator>
     <disk type='block' device='disk'>
       <driver name='qemu' type='raw'/>
       <source dev='/dev/VG1kvm/test_disk'/>
       <target dev='vda' bus='virtio'/>
     </disk>
     <disk type='block' device='disk'>
       <driver name='qemu' type='raw'/>
       <source dev='/dev/VG1kvm/test_boot'/>
       <target dev='vdb' bus='virtio'/>
     </disk>
   ...

/dev/VG1kvm/test_disk ("diskHD") has two partitions (1: /boot, 2:/)
/dev/VG1kvm/test_boot ("bootHD") has one partition (1: /boot)

The MasterBootRecord is saved on diskHD.
The /boot on diskHD is not used (anymore).
The /boot on bootHD should be used instead.
GRUB complains about the UUID of this bootHD.

It is possible to start the VM from
a) a live CD (Knoppix 9.2), where 'cat /proc/partitions' lists all
defined partitions
b) a Debian 11.1 netinst ISO

It is possible to install a new system from the netinst-ISO into an
image file,
BUT this newly created system in the VM does not boot either. It hangs
in GRUB rescue mode as described above.

So the disks generated by libvirt/kvm/qemu can be detected (Knoppix,
Debian-netinst), but they are not by GRUB.

Any ideas how to fix this (and which package)?

Thanks in advance!
Ulrich

Note:
The behaviour described above was observed after the upgrade from Buster
to Bullseye (e.g.: with libvirt-daemon 7.0.0).
The system information below was generated by reportbug after
re-installing Debian Buster. In this setup everything works again.
#1000496#10
Date:
2021-12-23 20:12:40 UTC
From:
To:
Hi Ulrich,

Sorry it took so long to get back to you.

I don't know for sure, but leaving it under upgrade-reports are not
going to draw much eyes. Let's try with the grub2 maintainers. Maybe
they have a clue and know where to reassign if this doesn't look like an
issue with grub2?

Paul