Re: EFI and Xen

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

On Tue, May 13, 2025 at 10:59:13PM -0400, Chuck Zmudzinski wrote:
> On 2/13/2025 10:54 AM, César Catrián C. wrote:
> > Hello,
> > 
> > 
> > I am migrating a Xen NetBSD 10 system to a new hardware and I would like to know if EFI is supported for XEN to pass on the vga console for keeping on loading the kernel.
> > 
> > That's because after Xen loading stage at boot, reach the stage of relinquishing VGA console, it goes blank.
> > 
> > If there is no solution just I will return to legacy boot.
> > 
> > 
> > Kind regards
> 
> Hi,
> 
> I am seeing the same problem, but my system is so new that, unfortunately, legacy BIOS boot is not supported at all on the system, it is truly a UEFI-only system.
> 
> The system has an Intel Raptor Lake i5-14500 CPU, and it is configured to boot several systems, such as Fedora, Windows, Alma Linux, and Xen with the various Linux distros. Xen works well with various flavors of Linux Dom0 on the box. I decided to try out NetBSD 10.1, and I got NetBSD 10.1 with the GENERIC amd64 kernel booting on bare metal using UEFI.
> 
> So I followed the guide for port netbsd/xen by installing the Xen 4.18 kernel and tools from pkgsrc and adding a boot option for Xen to boot.cfg using the "load" command for the netbsd-XEN3_DOM0 kernel and the "multiboot" command for the Xen kernel.
> 
> When I try it I can see that the bootloader loads the Xen kernel and the Xen kernel displays some messages on the VGA console. Then I see that the bootloader loads the netbsd-XEN3_DOM0 kernel, but before any kernel messages are displayed from the netbsd DOM0 kernel the screen goes blank for several seconds and then falls back to the default UEFI boot option on the system, which happens to be grub2-efi for Fedora. That is normal behavior for the UEFI on my box: When the selected non-default boot option fails spectacularly, it just gives up and falls back to the default UEFI boot option.
> 
> So, is netbsd/xen supposed to work with UEFI booting, or are there issues? I saw this commit which I thought might have enabled support for booting netbsd/xen on UEFI-only systems back in 2019:


I have a server using EFI with Xen and NetBSD dom0. I use the NetBSD boot
loader with:
menu=Boot Xen PV:load /netbsd console=pc root=dk1; multiboot /xen-debug.gz dom0_mem=8192M console=com1,vga com1=115200,8n1 conring_size=4096k sync_console

If you have a serial console it may be worth a try, to get more messages.
There are also Xen options to help debug this kind of issue (like:
don't give the VGA console to dom0, delay before reboot and so on).
If Xen keeps the VGA console, use console=com0 for NetBSD so that
it sends it boot messages to Xen.

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