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Re: [Xen-devel] [PATCH] libxc: set CPUID topology leaf as unsupported fo

To: "David Vrabel" <david.vrabel@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] libxc: set CPUID topology leaf as unsupported for PV guests
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Fri, 15 Jul 2011 09:41:54 +0100
Cc: Keir Fraser <keir.xen@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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>>> On 14.07.11 at 16:25, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> On 14/07/11 14:30, Keir Fraser wrote:
>> On 14/07/2011 12:50, "David Vrabel" <david.vrabel@xxxxxxxxxx> wrote:
>>> libxc: set CPUID topology leaf as unsupported for PV guests
>>> The result of a CPUID Extended Topology Enumeration leaf for PV guests
>>> is invalid as the level in ECX is ignored.  This can cause some guests
>>> to loop endlessly when trying to enumerate the topology.
>>> Since the physical topology isn't useful to PV guests set the topology
>>> leaf as unsupported.
>> For future reference, you also need to modify
>> xen/arch/x86/traps.c:pv_cpuid(), for dom0.
> Looking at the code it looks like dom0 would at least see valid data for
> the the topology leaf.  But I guess the info makes no sense to dom0 as
> well as domU guests.  Patch sent if you've not already fixed it up.

It may make limited sense to Dom0 if "dom0_vcpus_pin" is in effect.


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