Re: running xen on current

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, Apr 15, 2021 at 01:39:37PM +0100, Patrick Welche wrote:
> 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?

It should be; but there are probably differences between BIOS and EFI, even
when using multiboot (the way to access the console, or find the ACPI
tables, may be different, for example)

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--