VT-D Register specificaiton Questions

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VT-D Register specificaiton Questions

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I'm trying to understand Vt-D as I am interested in VT-d register-level programming....

Two parts of the Vt-D specification are a bit unclear to me:

- When the "Translation Enable (TE)" bit is CLEAR in the "GCMD_REG", does this mean that all DMA transactions are allowed? (outside of the areas potentially protected by the "Protected Memory Range Registers")? Or does it mean *no* DMA transactions are allowed? I'm mainly interested in the case for "Legacy Mode Address Translation.

- What is the meaning of "Execute Permission" for device translation requests? Although this seems analogous to page table permissions, this seems weird to me as I don't think of HW devices "executing instructions" from system memory (and even if they did, why does an IOMMU care?).

Thanks!

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