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

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Message-ID: <86802c440803251605w7021b60cmbc312eb9ca87d277@mail.gmail.com>
Date:	Tue, 25 Mar 2008 16:05:27 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Venki Pallipadi" <venkatesh.pallipadi@...el.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"kernel list" <linux-kernel@...r.kernel.org>,
	suresh.b.siddha@...el.com
Subject: Re: [PATCH] x86: pat cpu feature bit setting for known cpus

On Tue, Mar 25, 2008 at 4:01 PM, H. Peter Anvin <hpa@...or.com> wrote:
>
> H. Peter Anvin wrote:
>  > Ingo Molnar wrote:
>  >> * Venki Pallipadi <venkatesh.pallipadi@...el.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.
>  >
>
>  By the way, I want to clarify: I didn't mean it was *intended* as
>  vendor-lockin, just that it's an undesirable effect of this.

if the PAT works, we may need to trim the memory according to MTRR, right?

YH
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