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

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Date:	Thu, 18 Jun 2009 11:50:57 -0700
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	'Muli Ben-Yehuda' <muli@...ibm.com>,
	'Chris Wright' <chrisw@...hat.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

>
>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.

The device in kvm is attached to a kvm domain by intel_iommu_attach_device(). In this function, domain_context_mapping() changes the device's domain to kvm domain from si_domain.

Actually there is a bug when a device is detached from kvm domain...in intel_iommu_detach_device(), I should assigned the device back to the si_domain. So the device can be used in native again.

Thanks.

-Fenghua

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