[CRIU] [PATCH 06/15] cpuinfo: x86 -- Add dump and validation

[Pavel Emelyanov]

On 09/23/2014 11:20 PM, Cyrill Gorcunov wrote:
> On Tue, Sep 23, 2014 at 11:07:01PM +0400, Pavel Emelyanov wrote:
>>
>> OK. Let's imagine the cpu has 
>>
>>    X86_FEATURE_XMM4_1 | X86_FEATURE_XMM4_2 | A
>>
>> and we ask it to check the image which contains 
>>
>>    X86_FEATURE_XMM4_1 | B
>>
>> and let's assume that A == B. Will the checker fail? Should it? Why?
> 
> Sure it fails, and sure more precise feature deps inspection is needed
> but as first iteration I think it's fine having plain memcmp here.

I still don't understand why "cpu.mask >= image.mask -> validation OK"
receipt doesn't work. If I'm not mistaken, we've been using this logic
in OpenVZ's and PCS vzmigrate for many years.

> As to should it -- I don't know, technically the cpu itself is
> backward compatible (at least it should be) but if someone migrate
> to feature rich cpu , the dump it here and migrate back -- he will
> have unpleasant surprise

Why?

> in restore failure and will have to pass
> --cpu-cap none or something to ignore new feature mask obtained
> from remote cpu. Thus lets require complete match for feature bits
> and relax it in future if needed.
> .
>