From: Andi Kleen <andi@firstfloor.org>
Subject: Re: [PATCH 00 of 36] x86/paravirt: groundwork for 64-bit Xen support
Date: Wed, 25 Jun 2008 14:40:20 +0200
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In-Reply-To: <patchbomb.1214367536@localhost> (Jeremy Fitzhardinge's message of "Wed, 25 Jun 2008 00:18:56 -0400")
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To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Mark McLoughlin <markmc@redhat.com>, xen-devel <xen-devel@lists.xensource.com>, Eduardo Habkost <ehabkost@redhat.com>, Stephen Tweedie <sct@redhat.com>, LKML <linux-kernel@vger.kernel.org>
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Jeremy Fitzhardinge <jeremy@goop.org> writes:
>
> This moves __PAGE_OFFSET up by 16 GDT slots, from 0xffff810000000000

GDT?  PDP?

> to 0xffff880000000000.  I have no general justification for this: th

This will significantly decrease the maximum amount of physical
memory supported by Linux longer term.

> "x86_64: PSE no longer a hard requirement."
>
> Because booting under Xen doesn't set PSE, it's no longer a hard
> requirement for the kernel.  PSE will be used whereever possible.

Both sound like cases of "let's hack Linux to work around Xen 
problems"

-Andi