Re: Xen boot strangeness (Was: Re: [SOLVED] Re: Xen 4.18.5_20250521nb0 not ELF binary (Was: Re: EFI and Xen))

[Chuck Zmudzinski <frchuckz%gmail.com@localhost>]

On 5/29/2025 5:27 PM, Greg A. Woods wrote:
> At Thu, 29 May 2025 16:30:39 -0400, Chuck Zmudzinski <frchuckz%gmail.com@localhost> wrote:
> Subject: Re: Xen boot strangeness (Was: Re: [SOLVED] Re: Xen 4.18.5_20250521nb0 not ELF binary (Was: Re: EFI and Xen))
>>
>> Ok, let's see what happens. I use this boot command line:
>>
>> menu=Boot normally with Xen:dev hd2d:;load /netbsd-XEN3_DOM0.gz -c console=xencons bootdev=wd1;multiboot /xen.gz dom0_mem=2G dom0_max_vcpus=4 com1=9600,8n1,0x40c0,16,1:0.0 console=com1 cet=no-ibt pv-l1tf=false
>>
>> Only difference from the one that works is that I do a s/com2/com1/g
>>
>> Still, DOM0 sees the serial port that Xen is using as com2, not com0, so
>> with this configuration it still crashes unless I disable com* using userconf.
>>
>> So it behaves exactly the same as when I told Xen the console is com2 instead of com1.
> 
> Ah, that's unfortunate.
> 
> I started looking to see how the normal ISA COM ports are "hidden" from
> the guest dom0 kernel, but I can't seem to find the right code.
> 
> I do find calls to pci_hide_device() for the debug device drivers, but
> not for the console, and of course those are only for PCI devices.
> 
> I need to do more searching to see how that works, and maybe then I'll
> see why it isn't hiding the PCI serial device used by the console.

It seems to me our DOM0 config assumes Xen is not successfully hiding the
serial console used by Xen from DOM0, not even the normal ISA com ports,
and that is why we comment out com0 in the XEN3_DOM0 config. If Xen was
hiding that device from DOM0, we would not need to do that would we?

If we could fix this on the Xen side by hiding whatever com device Xen is
using for its console, whether that be a normal com device, a PCI device,
AMT device or whatever, that would be great.