Re: [PATCH 1/2] IOMMU Identity Mapping Support:iommu_identity_mapping definition

From: Muli Ben-Yehuda
Date: Thu Jun 18 2009 - 14:29:03 EST

On Thu, Jun 18, 2009 at 11:14:51AM -0700, Yu, Fenghua wrote:
> >
> >On Thu, Jun 18, 2009 at 11:05:14AM -0700, Fenghua Yu wrote:
> >
> >> IOMMU Identity Mapping Support: iommu_identity_mapping definition
> >>
> >> Identity mapping for IOMMU defines a single domain to 1:1 map all
> >> pci devices to all usable memory.
> >
> >Why use VT-d at all in this case? Do you have a use-case in mind?
> Some users want to use VT-d in KVM but are concerned of DMA
> remapping performance. They can use identity mapping and still have
> KVM on VT-d. They can also use pass through patch (sent out before)
> if hardware supports pass through.

Sorry, I must be missing something. For the normal device assignment
case, we want the IOMMU page tables to have gpa->hpa mappings rather
than the 1-1 identity mapping. How do you envision the 1-1 mapping
being used in the device assignment case?

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