Re: [PATCH] x86: pat cpu feature bit setting for known cpus

["H. Peter Anvin" <hpa@zytor.com>]

Ingo Molnar wrote:
> * Venki Pallipadi <venkatesh.pallipadi@intel.com> wrote:
> 
>>>>  OK, note previous question: what is the motivation for having 
>>>>  this as a whitelist (as opposed to a blacklist)?
>>> Venkatesh could tell?
>> Main reason for white-list at this point is not to be side-tracked by 
>> real or potential erratas on older CPUs. Focussing on getting the 
>> support for this feature on current and future CPUs. If older CPUs 
>> have survived all these days without this feature, they should be 
>> doing OK.
> 
> well, the upside would be that since most testing of Linux kernels is 
> done on _old_ hardware (people tend to risk their old hw first ;-), we'd 
> get faster convergence of the codebase, even though we have the risk of 
> erratas (known and unknown ones alike). Code that artificially limits 
> its utility is almost always slow to stabilize.
> 

Yes, using a whitelist of this type is wrong, IMO, and smells faintly of 
vendor-lockin.

	-hpa