linux-kernel - Re: [PATCH 4/4] x86, gart: Make sure GART does not map physmem above 1TB

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Message-ID: <20110418145230.GH2192@amd.com>
Date:	Mon, 18 Apr 2011 16:52:30 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...nel.org" <stable@...nel.org>
Subject: Re: [PATCH 4/4] x86, gart: Make sure GART does not map physmem
 above 1TB

On Mon, Apr 18, 2011 at 10:46:24AM -0400, H. Peter Anvin wrote:
> On 04/18/2011 06:45 AM, Joerg Roedel wrote:
> > The GART can only map physical memory below 1TB. Make sure
> > the gart driver in the kernel does not try to map memory
> > above 1TB.
> 
> Where does this limit come from?

>From the hardware. A GART PTE is only 32 bits in size so that it cannot
be expanded. The physical address bits 32-39 are mapped 11:4 in the PTE.
This can not be architecturally expanded to more than 40 physical bits.

Regards,

	Joerg

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