4.15.0-rc3 can't create domain when dom0 uses newer kernel

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

Hi all,

I've ran into a pretty strange issue. I have a freshly installed 4.15.0-rc3 system and everything works fine with the stock Ubuntu 20.04 vmlinuz-5.4.0-66-generic as the dom0 kernel - except vmtrace, which needs a newer kernel, that's expected. Now if I boot dom0 with vmlinuz-5.8.0-44-generic or vmlinuz-5.10.0-1016-oem I can't start any domains because of some strange disk error:

root@t2:/shared/cfg# xl create ubuntu-20.04.cfg
Parsing config from ubuntu-20.04.cfg
libxl: error: libxl_device.c:1109:device_backend_callback: Domain 1:unable to add device with path /local/domain/0/backend/vbd/1/51712
libxl: error: libxl_create.c:1613:domcreate_launch_dm: Domain 1:unable to add disk devices
libxl: error: libxl_device.c:1109:device_backend_callback: Domain 1:unable to remove device with path /local/domain/0/backend/vbd/1/51712
libxl: error: libxl_domain.c:1529:devices_destroy_cb: Domain 1:libxl__devices_destroy failed
libxl: error: libxl_domain.c:1182:libxl__destroy_domid: Domain 1:Non-existant domain
libxl: error: libxl_domain.c:1136:domain_destroy_callback: Domain 1:Unable to destroy guest
libxl: error: libxl_domain.c:1063:domain_destroy_cb: Domain 1:Destruction of domain failed

This is the disk config:

disk = ['phy:/dev/t2vg/ubuntu-20.04,xvda,w']

It's a standard LVM volume that is active, lvscan shows:

  ACTIVE            '/dev/t2vg/ubuntu-20.04' [40.00 GiB] inherit

I checked all the logs and I don't see anything relevant anywhere. If I reboot the system with the older kernel everything works as expected as far as creating the same domain with the same config.

Anyone has any idea what might be going on here?

Thanks,

Tamas