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Message-ID: <A6AD88C3F2289247BE726C37303E1EB8B0044F7D@orsmsx505.amr.corp.intel.com>
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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