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Re: [Xen-devel] PAE, Elf headers, and Extended CR3 registers

To: Randy Thelen <rthelen@xxxxxxxxxx>
Subject: Re: [Xen-devel] PAE, Elf headers, and Extended CR3 registers
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sat, 16 Sep 2006 17:04:32 +0100
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Thread-topic: [Xen-devel] PAE, Elf headers, and Extended CR3 registers
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On 15/9/06 8:40 pm, "Randy Thelen" <rthelen@xxxxxxxxxx> wrote:

> My concern had been that 'extended CR3' implied hardware support for
> a 64 bit CR3 register.  Instead it means that I shouldn't really care
> if the mfn of my Page Table Directory Pointer is above 4GB, Xen will
> handle the condition for me.  And, the way I'll decode the mfn, if
> necessary (which I would agree should be rare), would be with those
> macros.

Yes, that's correct. You *must* decode/encode any CR3 value passed to/from
Xen using those macros or you simply will not work properly on >4GB systems.
Luckily, as I pointed out for Linux, this will probably only be an issue you
come across when initialising secondary VCPUs.

 -- Keir

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