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

From: Muli Ben-Yehuda
Date: Thu Jun 18 2009 - 14:44:32 EST

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.

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