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An IOMMU provides virtual address spaces to other devices. Traditionally devices able to do Direct Memory Access (DMA masters) would use bus addresses, allowing them to access most of the system memory. An IOMMU limits their scope, enforcing address ranges and permissions of DMA transactions. The virtio-iommu device manages Direct Memory Access (DMA) from one or more physical or virtual devices assigned to a guest.
Potential use cases are:
Limit guest devices' scope to access system memory during DMA (e.g. for a pass-through device).
Enable scatter-gather accesses due to remapping (DMA buffers do not need to be physically-contiguous).
- 2-stage IOMMU support for systems that don't have relevant hardware.
Device ID.
REQ-1: The device ID MUST be set according to the requirement in chapter 2.1 in [VIRTIO-IOMMU].
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