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Message-ID: <86802c440803251605w7021b60cmbc312eb9ca87d277@mail.gmail.com>
Date: Tue, 25 Mar 2008 16:05:27 -0700
From: "Yinghai Lu" <yhlu.kernel@gmail.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] x86: pat cpu feature bit setting for known cpus
Cc: "Ingo Molnar" <mingo@elte.hu>,
       "Venki Pallipadi" <venkatesh.pallipadi@intel.com>,
       "Thomas Gleixner" <tglx@linutronix.de>,
       "Andrew Morton" <akpm@linux-foundation.org>,
       "kernel list" <linux-kernel@vger.kernel.org>, suresh.b.siddha@intel.com
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On Tue, Mar 25, 2008 at 4:01 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>
> H. Peter Anvin wrote:
>  > 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.
>  >
>
>  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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