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

[Yu, Fenghua]

>
>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.

By default, identity mapping is turned off. "iommu=identity" can turn it on

Thanks.

-Fenghua
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