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Re: [Xen-devel] [PATCH] supporting non-NX/XD capable processors on x86_6

To: "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] supporting non-NX/XD capable processors on x86_64 xenlinux
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Thu, 18 Aug 2005 16:09:34 +0100
Cc: Jerone Young <jerone@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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On 18 Aug 2005, at 15:15, Nakajima, Jun wrote:

One obvious reason is: xen-specific drivers are using __PAGE_KERNEL (and
they don't exist in the native Linux). If xen_contig_memory, for
example, does not work, it won't boot... Fixing xen_contig_memory did
not fix the booting problem as long as I remember?

Yeah, I see what you mean. I've just applied a patch that cleans up the few remaining bad spots where we weren't using pfn_pte() or pfn_pte_ma() constructors. I can now boot okay even with NX/XD disabled in Xen.

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?

 -- Keir

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