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

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Message-ID: <20080627222931.GB7201@il.ibm.com>
Date:	Fri, 27 Jun 2008 18:29:31 -0400
From:	Muli Ben-Yehuda <muli@...ibm.com>
To:	"Duran, Leo" <leo.duran@....com>
Cc:	Joerg Roedel <joro@...tes.org>, 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 Fri, Jun 27, 2008 at 03:39:31PM -0500, Duran, Leo wrote:

> 2) IOMMU will not translate if the exclusion range has been enabled, and
> the DMA address falls inside that range.
> The exclusion range can be enabled for specific devices, or for all
> devices... Enabling the exclusion range can be considered a 'performance
> optimization' (no table-walks), with the caveat of not being able to
> provide protection for devices sharing the exclusion range (BTW, there's
> a single exclusion address range per IOMMU).

So, if I understand this correctly, could we implement Joerg's
"almost-direct-map" by having 0-64MB translated for host-owned
devices, and then 64MB-end excluded (again, for host-owned devices
only)? If yes, it should provide a small boost in performance (may or
may not be measurable) over having 64MB-end be an identity
translation.

Cheers,
Muli
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