linux-kernel - RE: [PATCH 01/34] AMD IOMMU: add Kconfig entry

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Date:	Sat, 28 Jun 2008 09:40:57 -0500
From:	"Duran, Leo" <leo.duran@....com>
To:	"Joerg Roedel" <joro@...tes.org>
CC:	"Muli Ben-Yehuda" <muli@...ibm.com>,
	"Adrian Bunk" <bunk@...nel.org>,
	"Richter, Robert" <rrichter@...e.amd.com>,
	<linux-kernel@...r.kernel.org>, <iommu@...ts.linux-foundation.org>,
	"Andi Kleen" <andi@...stfloor.org>,
	"Biemueller, Sebastian" <Sebastian.Biemueller@....com>,
	<tglx@...utronix.de>, <mingo@...hat.com>,
	"Sarathy, Bhavna" <Bhavna.Sarathy@....com>
Subject: RE: [PATCH 01/34] AMD IOMMU: add Kconfig entry

On Saturday, June 28, 2008 6:04 AM, Joerg Roedel wrote:

> Yes, there is only one exclusion range per IOMMU. The problem is that
> an
> exclusion range from 64MB to the end may not be possible because there
> is
> an exclusion range already configured in the ACPI table. On my System
> for
> example the exclusion range is somewhere in the first megabyte of RAM.
> In this case the direct mapping using page tables is needed. If there
> is
> no exclusion range defined in ACPI this idea would work of course.
> 
> Joerg
> 

Direct 1:1 mappings have a couple of issues:
1) They don't provide a performance optimization (i.e., table-walk still
required)
2) Your aperture would have to be large enough so that virtual==physical
(i.e., lots of memory for page-tables)

Leo.


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