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Re: [Xen-devel] [PATCH][HVM] fix migration from NX-capable machine to no

To: David Lively <dlively@xxxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH][HVM] fix migration from NX-capable machine to non-NX-capable machine
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 28 Sep 2007 08:18:13 +0100
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Thread-topic: [Xen-devel] [PATCH][HVM] fix migration from NX-capable machine to non-NX-capable machine
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On 27/9/07 22:12, "David Lively" <dlively@xxxxxxxxxxxxxxx> wrote:

> The attached patch (to 3.1.1-rc2) fixes a hypervisor crash that we're
> seeing when migrating a HVM guest from a machine that supports the NX
> bit to one that doesn't (e.g., because it's disabled in the BIOS).  It
> keeps the guest copy of EFER "as is", so the guest will see EFER_NX if
> it previously set it -- we just won't propagate this EFER bit to a
> non-NX-capable host.

Actually this issue is very nearly handled by xen-3.1-testing:15064 and
xen-unstable:15066. The HVM state load code that sets guest efer should barf
on !cpu_has_nx && EFER_NX, just as the wrmsr-handling code does.

 -- Keir

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