[Xen-devel] RE: Live migration fails due to c/s 20627

["Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>]

Keir Fraser wrote:
> On 14/12/2009 18:02, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>
> wrote: 
> 
>> This may be true in concept, but existing tools (including
>> the default xm tools) do NOT check for this... I just
>> tested a live migration between a Nehalem (which supports
>> rdtscp) and a Conroe (which does not).  The live migration
>> works fine and the app using rdtscp runs fine on the
>> Nehalem and then crashes when the live migration completes
>> on the Conroe.  I *know* of existing code in Oracle
>> that will be broken by this!
> 
> This is a general problem for migration between dissimilar
> processors. The solution is to 'level' the feature sets, by masking
> CPUID flags from the more-featured processor. In this case you would
> mask out RDTSCP (and perhaps others too). This does need the RDTSCP
> flag setting/clearing to be moved to xc_cpuid_x86.c, as currently the
> user cannot override the policy wedged into the hypervisor itself.
> That's an easy thing to fix. 

I will write a patch for this. Thanks!

-- Dongxiao

> 
>  -- Keir
> 
> 
> 
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