Re: Problems booting Ubuntu Jammy 22.04 PV domU from Jammy dom0

[James Dingwall <james-xen@xxxxxxxxxxxxxx>]

On Wed, Apr 27, 2022 at 12:01:54AM +0200, Klaus Darilion wrote:
> Hello! Our setup ir probably antic but reliable. We build PV domU with 
> xen-create-image (fuly automatic with Puppet).
> 
> Just today I built the first Jammy domU on a Jammy dom0 (Linux 5.15 with 
> xen-hypervisor-4.16-amd64 and xen-tools 4.9.1). Building the domU worked 
> fine, but I can not start the domU:
> 
> When using pygrub the error is:
> xc: error: panic: xg_dom_bzimageloader.c:619: xc_try_zstd_decode: ZSTD 
> decompress support unavailable
> 
> So it seems that pygrub does not support the ZSTD compressed kernel.
> 
> So I tried to boot the domU with pvgrub2 by setting:
> kernel = "/usr/lib/grub-xen/grub-x86_64-xen.bin"
> 
> This brings me to a Grub shell, and manuall booting just leads to:
> grub> linux /boot/vmlinuz root=/dev/xvda2
> error: not xen image.
> 
> https://wiki.xenproject.org/wiki/Xen_Project_4.15_Feature_List states 
> "Support for zstd-compressed dom0 (x86) and domU kernels.".
> 
> So I need some advice/confirmations:
> Can I boot Linux 5.15 (ZSTD kernel) with pygrub? If not, is it planned to add 
> ZSTD support to pygrub?
> 
> If pygrub will not support ZSTD, what are my options? Should it work with 
> pvgrub2 and I am doing something wrong? How to correctly use pvgrub2.
> 
> If pvgrub2 does not support ZSTD, what are my options? Would it help to move 
> from PV to PVH,PVHVM,...? Can I automate building domUs similar to 
> xen-create-image also with non-PV domUs?
> 
> Thanks
> Klaus

For my focal based environment I can boot guests with the HWE kernel using
zstd with these options:

  type = 'pvh'
  kernel = '/usr/lib/grub-xen/grub-i386-xen_pvh.bin'

For guests that need to be 'pv' then I've had to decompress the kernel image
using the extract-vmlinux which is part of the kernel sources.

James