Re: [Xen-users] cpuid masking on Xen 4.1

[Charles Koprowski <cko@xxxxxxxxxxx>]

Hi,

2016-03-23 13:14 GMT+01:00 Andrew Cooper <andrew.cooper3@xxxxxxxxxx>:
> On 23/03/16 11:46, Roger Pau Monné wrote:
>> On Fri, 11 Mar 2016, Charles Koprowski wrote:
>>> Do all CPUs support CPUID masking ? In my case I'm trying on Intel
>>> Xeon E7-4850 v3
>
> This is a Hawell processor, and doesn't have cpuid masking.  It has
> cpuid faulting instead.
>
>> I'm not really familiar with with cpuid leveling, but I think there's
>> indeed something wrong. I would expect that having cpu_has_cpuid_faulting
>> means we would do the masking somewhere else (in the fault handler), but I
>> cannot find any usages of opt_cpuid_mask_* anywhere outside of the intel
>> and amd cpu initialization files.
>
> If you look in the XenServer patch queue
> (https://github.com/xenserver/xen-4.6.pg/) at a changeset older than
> b39aebaf663395714ffcff19e9707500a1580d3f, you will find
> xen-apply-cpuid-mask-to-cpuid-faulting.patch which causes the cpuid
> masks to apply to faulting as well.
>
> All of this however has been superseded by my cpuid improvement series
> which is currently at v3 and expected to land in Xen 4.7.
>
> What are you actually trying to do?

I'm running a cluster of 4 hosts that run Xen 4.1 and share a
clustered LVM group. They all have Intel Xeon E5-4620 CPU (Dell PE
R820) and run Ubuntu 12.04

I'm currently extending the cluster with a brand new Dell PE R930
which have Intel Xeon E7-4850 v3 (unfortunately R820 serie has been
discontinued).

So I'm trying to "downgrade" the R930 CPU in order to be able to use
live migration. Currently when I initiate a live migration from the
R930 to one of the other hosts, the whole machine freeze without
raising any message. I thought that only the guest OS would crash
instead...

Do you think I can run a much recent version of Xen on the R930 and be
able to use live migration with the rest of the cluster ?

I also tried setting the cpuid option at guest level configuration but
didn't manage to mask all unwanted CPU features.

Thanks,

Regards
-- 
Charles Koprowski

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