From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gerd Hoffmann <kraxel@redhat.com>
Subject: Re: Re: Continuing problems booting
Date: Mon, 09 Mar 2009 16:56:52 +0100
Message-ID: <49B53C44.1090706@redhat.com>
References: <alpine.GSO.2.00.0902201239010.757@algedi.dur.ac.uk>	<alpine.GSO.2.00.0902201554500.757@algedi.dur.ac.uk>	<alpine.LFD.2.00.0902211225540.14632@vega4.dur.ac.uk>	<49A0F68D.9070306@goop.org>	<alpine.LFD.2.00.0902220922040.4149@vega1.dur.ac.uk>	<alpine.LFD.2.00.0902221449410.17196@vega3.dur.ac.uk>	<49A187B8.7000902@goop.org>	<alpine.LFD.2.00.0902222257230.4472@vega4.dur.ac.uk>	<49A1DD80.1080903@goop.org>	<alpine.LFD.2.00.0902222359090.4472@vega4.dur.ac.uk>	<49A241EC.3050300@goop.org>	<alpine.LFD.2.00.0902242228550.12607@vega3.dur.ac.uk>	<alpine.LFD.2.00.0902272317030.17305@vega3.dur.ac.uk>
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Gerd Hoffmann wrote:
> i.e. early iomap setup is different in 32bit and 64bit.  Which would
> also explain why vgacon works just fine in 64bit mode.

I think it is something else.

arch/x86/mm/init_64.c, phys_pte_init():

        /*
         * We will re-use the existing mapping.
         * Xen for example has some special requirements, like mapping
         * pagetable pages as RO. So assume someone who pre-setup
         * these mappings are more intelligent.
         */
        if (pte_val(*pte)) {
                pages++;
                continue;
         }

I think that does also make sure vga mappings are not overwritten with
something else.  32bit seems to have no equivalent for this though ...

cheers,
  Gerd