Re: [PATCH] X86: don't report PAT on CPUs that don't support it

From	"H. Peter Anvin" <hpa@zytor.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] X86: don't report PAT on CPUs that don't support it
Date	2017-05-16 16:10 +0200
Message-ID	<tHLkK-6BF-5@gated-at.bofh.it> (permalink)
References	<txGFI-1tx-19@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 04/18/17 12:07, Mikulas Patocka wrote:
> 
> However, on AMD K6-3 CPU, the processor initialization code never calls
> pat_init() and so __pat_enabled stays 1 and the function pat_enabled()
> returns true, even though the K6-3 CPU doesn't support PAT.
> 

OK, now I'm wondering: are you actually *using* said K6-3 machine, and
if so, are you actually dependent on write combining on it?  The reason
I'm asking is because I would personally like to completely remove the
support for using MTRRs to create WC mappings, as it only affects a
handful of ancient CPUs: Pentium Pro, Pentium II, K6-*, and possibly
some Cyrix/Centaur part.  Earlier CPUs didn't have WC, but could set WB,
WT or UC via the page tables without needing the PAT MSR, and newer CPUs
have PAT.

	-hpa

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Re: [PATCH] X86: don't report PAT on CPUs that don't support it "H. Peter Anvin" <hpa@zytor.com> - 2017-05-16 16:10 +0200
  Re: [PATCH] X86: don't report PAT on CPUs that don't support it Mikulas Patocka <mpatocka@redhat.com> - 2017-05-16 17:50 +0200
    Re: [PATCH] X86: don't report PAT on CPUs that don't support it Ingo Molnar <mingo@kernel.org> - 2017-05-18 09:20 +0200

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