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

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Date:	Thu, 18 Jun 2009 21:41:01 +0300
From:	Muli Ben-Yehuda <muli@...ibm.com>
To:	Chris Wright <chrisw@...hat.com>
Cc:	"Yu, Fenghua" <fenghua.yu@...el.com>,
	"'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

On Thu, Jun 18, 2009 at 11:31:21AM -0700, Chris Wright wrote:

> The 1-1 mapping is for all the host devices _not_ assigned to
> guests.  To eliminate the i/o overhead imposed on all guests not
> using an assigned device or from i/o from host.
>
> It's just the same as VT-d PassThrough mode for hardware that
> doesn't support it.

Ok, that makes sense. Thanks, Chris. However, that doesn't appear to
be what the patch does---unless I'm misreading, if
iommu_identity_mapping is set, *all* devices get identity
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.

Cheers,
Muli
-- 
Muli Ben-Yehuda | muli@...ibm.com | +972-4-8281080
Manager, Virtualization and Systems Architecture
Master Inventor, IBM Haifa Research Laboratory
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