Linear Aperture-Space Segments

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A linear aperture-space segment is similar to a linear memory-space segment. However, the aperture-space segment is only an address space and can't hold bits.

To hold the bits, system memory pages must be allocated, and the address-space range must be redirected to refer to those pages. The kernel-mode display miniport driver (KMD) must implement the DxgkDdiBuildPagingBuffer function for DXGK_OPERATION_MAP_APERTURE_SEGMENT and DXGK_OPERATION_UNMAP_APERTURE_SEGMENT operation types to handle the redirection and must expose this function as described in DriverEntry of Display Miniport Driver. Dxgkrnl calls DxgkDdiBuildPagingBuffer with the address-space range to be redirected and the MDL that references the physical system memory pages that were allocated.

The KMD typically accomplishes the redirection of the address-space range by programming a page table, which is unknown to the video memory manager (VidMm).

The driver must set the Aperture bit-field flag in the Flags member of the DXGK_SEGMENTDESCRIPTOR structure to specify a linear aperture-space segment. The driver can also set the following bit-field flags to indicate other segment support:

  • CpuVisible to indicate that the segment is CPU-accessible.

  • CacheCoherent to indicate that the segment maintains cache coherency with the CPU for the pages to which the segment redirects.

The following figure shows a visual representation of a linear aperture-space segment.

Diagram illustrating a linear aperture-space segment.