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Re: [Xen-devel] x86-64 machine_to_phys vs NX bit

To: Rik van Riel <riel@xxxxxxxxxx>
Subject: Re: [Xen-devel] x86-64 machine_to_phys vs NX bit
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 25 Aug 2006 16:27:03 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
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On 25/8/06 4:19 pm, "Rik van Riel" <riel@xxxxxxxxxx> wrote:

>> A long is only 32 bits there, so when we pass the MFN portion the NX bit is
>> conveniently truncated away!
> 
> Which means it'll do the wrong thing for machine addresses > 4GB
> on PAE, or am I overlooking something?

No, it gets shifted right 12 and *then* converted to a long. So you get a
44-bit addressing capability (32+12). But NX bit is bit 63, so it gets
truncated.

 -- Keir



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