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[Xen-devel] Re: [GIT PULL] xen /proc/mtrr implementation

To: Andi Kleen <andi@xxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [GIT PULL] xen /proc/mtrr implementation
From: "H. Peter Anvin" <hpa@xxxxxxxxx>
Date: Wed, 20 May 2009 16:03:23 -0700
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>, "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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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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