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Re: [Xen-devel] Re: [PATCH] supporting non-NX/XD capable processors on x

To: Jerone Young <jyoung5@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] supporting non-NX/XD capable processors on x86_64 xenlinux
From: Andi Kleen <ak@xxxxxxx>
Date: Thu, 18 Aug 2005 18:18:35 +0200
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Andi Kleen <ak@xxxxxxx>, Jerone Young <jerone@xxxxxxxxx>
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On Thu, Aug 18, 2005 at 11:05:42AM -0500, Jerone Young wrote:
> On Thu, 2005-08-18 at 17:51 +0200, Andi Kleen wrote:
> > Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> writes:
> > > 
> > > By the way -- from what I've seen of this NX/XD discussion so far, it
> > > sounds like even if CPUID says that NX/XD is supported, and you set
> > > the EFER.NXE bit, the BIOS can still cause this to be ignored! Is this
> > > true and, if so, what will happen if you try to use NX/XD anyway?
> > > i.e., will the bit be ignored, or will its use cause a page fault?
> > 
> > I don't think that can happen. When NX is disabled or not there it
> > doesn't appear in CPUID.
> Ah but it does:

Your example confirms what I said.


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