Subject: Re: [RFC][PATCH] linux-2.6.0-test2_mtrr-race-fix_A0
From: john stultz <johnstul@us.ibm.com>
To: Mathias =?ISO-8859-1?Q?Fr=F6hlich?= <Mathias.Froehlich@web.de>
Cc: lkml <linux-kernel@vger.kernel.org>
In-Reply-To: <200308061052.18550.Mathias.Froehlich@web.de>
References: <200308061052.18550.Mathias.Froehlich@web.de>
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Date: 06 Aug 2003 10:15:05 -0700
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On Wed, 2003-08-06 at 01:52, Mathias Fr?hlich wrote:
> Hi,
> 
> You should not remove the barrier past mtrr change. If you do that, it is 
> possible that cpu's run with inconsistent mtrrs. This can have bad 
> sideeffects since at least the cache snooping protocol used by intel uses 
> assumptions about the cachability of memory regions. Those information about 
> the cachability is also taken from the mtrrs as far as I remember.
> This intel cpu developer manual, which documented the early PII and PPro 
> chips, recommended this algorithm. Since actual intel cpus use the same old 
> cpu to chipset bus protocol, this old documentation most propably still 
> applies.

Hmm. I should dig up that doc. Its a little hazy in my mind, but I think
I understand your description. I'm glad you caught this, as I can't
imagine the subtle bugs that might have popped up. 

Well, let me look at it again and see if I can come up with a proper
fix. 

Thanks for the knowledgeable feedback and sanity checking!
-john

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