RE: [PATCH 01/34] AMD IOMMU: add Kconfig entry

[Duran, Leo]

On Saturday, June 28, 2008 6:04 AM, Joerg Roedel wrote:

> Yes, there is only one exclusion range per IOMMU. The problem is that
> an
> exclusion range from 64MB to the end may not be possible because there
> is
> an exclusion range already configured in the ACPI table. On my System
> for
> example the exclusion range is somewhere in the first megabyte of RAM.
> In this case the direct mapping using page tables is needed. If there
> is
> no exclusion range defined in ACPI this idea would work of course.
> 
> Joerg
> 

Direct 1:1 mappings have a couple of issues:
1) They don't provide a performance optimization (i.e., table-walk still
required)
2) Your aperture would have to be large enough so that virtual==physical
(i.e., lots of memory for page-tables)

Leo.


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