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From: "H. Peter Anvin" <hpa@zytor.com>
To: Mikulas Patocka <mpatocka@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] X86: don't report PAT on CPUs that don't support it
Date: Tue, 16 May 2017 06:57:07 -0700	[thread overview]
Message-ID: <235765f2-77dd-6210-17a1-ca67eecc5983@zytor.com> (raw)
In-Reply-To: <alpine.LRH.2.02.1704181501450.26399@file01.intranet.prod.int.rdu2.redhat.com>

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

  parent reply	other threads:[~2017-05-16 14:00 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-18 19:07 [PATCH] X86: don't report PAT on CPUs that don't support it Mikulas Patocka
2017-04-18 19:28 ` H. Peter Anvin
2017-04-18 20:47   ` Mikulas Patocka
2017-05-14 22:07     ` Mikulas Patocka
2017-05-16 13:57 ` H. Peter Anvin [this message]
2017-05-16 15:49   ` Mikulas Patocka
2017-05-18  7:17     ` Ingo Molnar
2017-05-24 10:21 ` [tip:x86/urgent] x86/PAT: Fix Xorg regression on CPUs that don't support PAT tip-bot for Mikulas Patocka
2017-05-28 18:18   ` Bernhard Held
2017-05-28 18:43     ` Andy Lutomirski
2017-05-29 22:50       ` Mikulas Patocka
2017-05-30 17:14         ` Dominik Brodowski
2017-05-30 17:59           ` Mikulas Patocka
2017-05-30 18:47             ` Dominik Brodowski
2017-05-30 19:30             ` Bernhard Held
2017-05-31  9:39             ` Junichi Nomura
2017-06-06 22:49       ` [PATCH v2] X86: don't report PAT on CPUs that don't support it Mikulas Patocka
2017-06-06 22:51         ` Andy Lutomirski
2017-06-06 23:21           ` Mikulas Patocka
2017-06-13 15:54             ` Andy Lutomirski
2017-06-14 20:24               ` Mikulas Patocka
2017-06-07 19:54         ` Bernhard Held
2017-07-03  5:05         ` Mikulas Patocka
2017-07-04 13:41           ` Thomas Gleixner
2017-07-04 13:48             ` Thomas Gleixner
2017-07-04 23:04             ` [PATCH v3] " Mikulas Patocka
2017-07-05  7:03               ` [tip:x86/urgent] x86/mm/pat: Don't " tip-bot for Mikulas Patocka

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