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

To: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>, "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 10:02:10 -0700
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Thread-topic: [Xen-devel] x86-64 machine_to_phys vs NX bit
Ian Pratt wrote:
>>> 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?
> Or we restrict 32b guests to the bottom 16 terabytes of memory. Please
> send me a machine for testing the patch :-)
> Ian

No, we don't :-) It cannot happen on the architecture implementations
that exist today. Maybe ASSERT() would be sufficient so that it can
remind us of the issues in years.

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