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

To:	"Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, "Rik van Riel" <riel@xxxxxxxxxx>
Subject:	RE: [Xen-devel] x86-64 machine_to_phys vs NX bit
From:	"Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
Date:	Fri, 25 Aug 2006 08:37:35 -0700
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Thread-topic:	[Xen-devel] x86-64 machine_to_phys vs NX bit

Keir Fraser wrote:
> 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.

Yes. For (on-going) 32-bit PV guests running on the 64-bit Xen, I guess
we should fix the convenient optimization now? 

> 
>  -- Keir

Jun
---
Intel Open Source Technology Center

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