linux-kernel - Re: [GIT PULL] xen /proc/mtrr implementation

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Message-ID: <4A148C3B.5050100@zytor.com>
Date:	Wed, 20 May 2009 16:03:23 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>, Ingo Molnar <mingo@...e.hu>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [GIT PULL] xen /proc/mtrr implementation

Andi Kleen wrote:
>>> Is this new interface only defined for swiotlb or MMIO mappings?
>>> If yes did you check the drivers only actually set it on
>>> swiotlb or MMIO (that seems dubious to me)?
>> Really?   Do we ever set unusual memory types on normal system memory?  
> 
> There were drivers at some point that set WC MTRRs on their
> transfer rings, not mmio.
> 
> Maybe these all switched to PAT now, maybe not

Most of those that I've heard of use WB memory and CLFLUSH.

The ones I know of which marked descriptor rings WB were ones which had
descriptor rings in MMIO space (which makes sense: MMIO reads are fully
synchronizing, but writes can be posted and write combined.)

	-hpa

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