Re: [Xen-devel] live migration from new platform to old platform

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.06.16 at 09:02, <xudong.hao@xxxxxxxxx> wrote:
> Guessing HVM context of some new instruction can't be restored to an old 
> platform. Current Xen xl has cupid parameter parsing implement "cupid" in 
> guest config, like 
> cupid='host,xsave=0'
> or
> cpuid=[ '1:ecx=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx0' ]
> 
> So I tried to disable some new cupid in guest config, both of the two below 
> method doesn't work, the HVM guest didn't disable those cupid such as "hle, 
> rtm, rdseed...".
> cpuid='host,3dnowprefetch=0,hle=0,rtm=0,rdseed=0,adx=0,smap=0'
> cpuid=['7:ebx=xxxxxxxxxxx000xxxxxx0xxxxxx0xxxx']

This derivation of yours doesn't look right: Leaf 7 requires a sub-leaf
to be specified (I don't recall off the top of my head what the exact
syntax is). So I first of all wonder - did you verify that your CPUID
adjustments actually too effect (in the sense of making it into
d->arch.cpuids[])? Because once there, I can't see how the guest
could get presented anything other than those values.

Jan


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