Re: running xen on current

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

On Thu, Apr 15, 2021 at 07:28:32AM -0400, Brad Spencer wrote:
> Manuel Bouyer <bouyer%antioche.eu.org@localhost> writes:
> 
> > On Thu, Apr 15, 2021 at 09:53:50AM +0100, Patrick Welche wrote:
> >> I have tried and failed to run xen on 3 -current/amd64 systems with
> >> 3 different failure modes:
> >> 
> >> 1) laptop:  xen.gz Building a PV Dom0 / ELF: not an ELF binary -> panic/reboot
> >> 2) desktop: XEN3_DOM0 panics including PR port-xen/55978
> >> 3) server:  Trampoline space cannot be allocated; will try fallback -> reboot
> >> 
> >> They are all working NetBSD-current/amd64 systems.
> >> 
> >> My conclusion was that xen is hopelessly broken, so was quite surprised
> >> by Greg Wood's thread about the finer points of running a guest OS, given
> >> that those systems won't even start the host OS.
> >> 
> >> I dug out an old desktop, and to my pleasant surprise it booted XEN3_DOM0,
> >> and I have managed to run some XEN3_DOMUs.
> >> 
> >> The difference between the working/broken setups seems to be that the
> >> working one is "BIOS" booting rather than EFI booting.
> >> 
> >> Among all your xen success stories, are any of you EFI booting?
> >
> > AFAIK EFI is not yet supported by Xen (maybe this is supported by 4.15,
> > I've not had a chance to try yet). I have it running on fairly recent
> > Dell servers (in BIOS mode)
> 
> 
> There has been fiddling with Xen and EFI for quite some time.  See:
> 
> https://wiki.xenproject.org/wiki/Xen_EFI
> 
> for example (might be old)... this indicates that Xen 4.3 or later could
> be built as a EFI binary and probably booted from the EFI firmware
> directly or with grub2 when grub2 is a EFI binary itself.  Of course
> those instructions are all Linux-centric and I don't know if you created
> a Xen kernel like this if it would boot a NetBSD DOM0 kernel.  I am in
> no position to try any tests with this right now personally, but it is
> tempting as I have a EFI only laptop that I could probably replace the
> hard drive temporarily.

Looking at

  https://xenproject.org/2021/04/08/xen-project-hypervisor-4-15/

(so 4.15 only just came out!) I see

  Unified boot images: It is now possible to create an image bundling
  together files needed for Xen to boot into a single EFI binary;
  making it now possible to boot a functional Xen system directly
  from the EFI boot manager, rather than having to go through grub
  multiboot.  Files that can be bundled include a hypervisor, dom0
  kernel, dom0 initrd, Xen KConfig, XSM configuration, and a device
  tree.

I thought that "go through grub multiboot" was the equivalent of our
boot.cfg "multiboot /xen.gz dom0_mem=1024M", but apparently not?
(Seems different to booting straight from the EFI boot menu)


Cheers,

Patrick