linux-kernel - RE: [PATCH 1/2] IOMMU Identity Mapping Support: iommu_identity

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Date:	Thu, 18 Jun 2009 12:09:56 -0700
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	'Chris Wright' <chrisw@...hat.com>,
	'Muli Ben-Yehuda' <muli@...ibm.com>
CC:	'David Woodhouse' <dwmw2@...radead.org>,
	'Linus Torvalds' <torvalds@...ux-foundation.org>,
	'Stephen Rothwell' <sfr@...b.auug.org.au>,
	'Andrew Morton' <akpm@...ux-foundation.org>,
	'Ingo Molnar' <mingo@...e.hu>,
	"Kay, Allen M" <allen.m.kay@...el.com>,
	'lkml' <linux-kernel@...r.kernel.org>,
	'iommu' <iommu@...ts.linux-foundation.org>
Subject: RE: [PATCH 1/2] IOMMU Identity Mapping Support:
	iommu_identity_mapping definition

>> mapping. Instead of a global command line option, we need to provide a
>> way to enable/disable pt or identity mapping (I agree that the user
>> shouldn't know or care which is used, the kernel should pick the best
>> one automatically) on a per BDF basis.
>
>Yeah, that's a possible enhancement.  Although once you've disabled one
>device's isolation you've created a hole...
>
The isolation hole is not much better than a global 1:1 mapping. If one device is 1:1 mapped to all memory. All of other devices can access part of this device's DMA range. And this device can access all of other devices' DMA range. Only better place than a global 1:1 mapping is all of other devices are isolated from each other.

Thanks.

-Fenghua
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