Re: [Qemu-devel] [PATCH RESEND v1 1/2] i386: Add Intel Processor Trace feature support

[Paolo Bonzini]

On 15/01/2018 08:19, Kang, Luwei wrote:
>> If you are forwarding host info directly to the guest, the feature
>> is not migration-safe.  The new feature needs to be added to 
>> feature_word_info[FEAT_7_0_EBX].unmigratable_flags.
>> 
> Hi, Thanks for you review. I want to support Intel PT live migration
> and patch [2/2] to do this. I don't understand  why need to add this
> feature in feature_word_info[FEAT_7_0_EBX].unmigratable_flags first
> to disable live migration.

Hi Luwei,

the issue is that different hosts can have different CPUID flags.  You
don't have a way to set the CPUID flags from the "-cpu" command line,
and it's not clear what values will be there in the various Ice Lake SKUs.

I am not sure if there is a mechanism to allow live migration only for
"-cpu host", but it cannot be supported for any other "-cpu" model.

Paolo