Re: [Qemu-devel] [PATCH v2 3/3] X86, mpx: Intel MPX xstate feature definition

[Liu, Jinsong]

H. Peter Anvin wrote:
> On 12/06/2013 12:05 PM, Liu, Jinsong wrote:
>>> 
>>> Since Peter already said the same, please undo these changes.
>>> 
>>> Also, how is XSTATE_EAGER used?  Should MPX be disabled when
>>> xsaveopt is disabled on the kernel command line?  (Liu, how would
>>> this affect the KVM patches, too?) 
>>> 
>>> Paolo
>> 
>> Currently seems no, and if needed we can add a new patch at kvm side
>> accordingly when native mpx patches checked in. 
>> 
> 
> We need to either disable these features in lazy mode, or we need to
> force eager mode if these features are to be supported.  The problem
> with the latter is that it means forcing eager mode regardless of if
> anything actually *uses* these features.
> 
> A third option would be to require applications to use a prctl() or
> similar to enable eager-save features.
> 
> Thoughts?
> 
>       -hpa

The third option seems better -- how does native mpx patches work, force eager?

Thanks,
Jinsong