From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: Xen hypervisor hangs on booting against c/s 16925
Date: Tue, 29 Jan 2008 11:58:20 +0000
Message-ID: <20080129115820.0b97573d@core>
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	<C3C4AE68.1B8DE%Keir.Fraser@cl.cam.ac.uk>
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To: Keir Fraser <Keir.Fraser@cl.cam.ac.uk>
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On Tue, 29 Jan 2008 10:20:24 +0000
Keir Fraser <Keir.Fraser@cl.cam.ac.uk> wrote:

> Isn't the memory map below 1MB well known, and no I/O exists down there
> except for VGA? Below that is conventional RAM; above that is ROM space.

Low 640K RAM
Above that ISA hole
Above that ROM (often shadowed into RAM)

Of the 640K RAM the low page is owned by the BIOS as are pages above the
EBDA. Some systems also use a 1 page EBDA to hide hardware bugs with
DMA prefetches running off the end of the 640K of RAM into I/O space.

The E820 map then tells you which bits of the 640K are owned by the BIOS
ACPI layer.

The ISA window is all non-cachable device mmio but rarely used for
anything but the PCI routed legacy VGA and MDA.

Alan