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

["Hao, Xudong" <xudong.hao@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Tuesday, June 7, 2016 3:39 PM
> To: Hao, Xudong <xudong.hao@xxxxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>; Zhang, Haozhong
> <haozhong.zhang@xxxxxxxxx>; Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> Subject: Re: [Xen-devel] live migration from new platform to old platform
> 
> >>> 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, Thanks.
Yes, there is a Sub-leaf after leaf 7, with below additional line, migration 
succeed from Broadwell to Haswell.
cpuid=['7,0:ebx=xxxxxxxxxxx000xxxxxx0xxxxxx0xxxx']

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