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List:       qubes-devel
Subject:    Re: [qubes-devel] Running (or not) Xen during installation
From:       Trammell Hudson <hudson () trmm ! net>
Date:       2016-11-03 20:51:38
Message-ID: 20161103205138.GD7965 () chishio ! swcp ! com
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On Thu, Nov 03, 2016 at 09:33:34PM +0100, Marek Marczykowski-Górecki wrote:
> On Thu, Nov 03, 2016 at 02:26:28PM -0600, Trammell Hudson wrote:
> > One other option is to use a minimal Linux image that can then kexec
> > Xen/dom0/initrd without any of the UEFI limitations. [...]
> 
> That's indeed interesting and in fact I was trying something like this
> when initially fighting with this UEFI problem. But every attempt to
> kexec Xen from Linux failed. How to do that?

I posted patches to the Xen list that remove dependencies on legacy BIOS
things like EBDA, although I don't think they have been (nor will they
be?) merged.  kexec of Xen was broken between Xen 3.1.0 and 3.1.3 almost a
decade ago and apparently no one else was sufficiently impacted by the
change to track it down:

https://lists.xen.org/archives/html/xen-devel/2016-08/msg01195.html

If there is an actual BIOS the VGA patches might not be necessary;
all of my test machines thus far are using coreboot with no legacy
support, so I haven't explored the minimal patch set to Xen.

> And how to pass dom0 kernel + initrd there?

kexec of a multboot kernel (like xen) allows multiple modules including
the kernel (and parameters) and the initrd.  You can see my Qubes
start script (run from Linux-as-bootloader in ROM) here:

https://github.com/osresearch/heads/blob/master/initrd/start-xen

> Will dom0 kernel started that way have access to UEFI
> runtime services - which is needed to setup bootloader parameters?

I'm not sure about that.  Again, none of my test machines have any
legacy firmware nor any traditional bootloaders, so I haven't explored
how it interacts with those pieces.

-- 
Trammell

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