+ * The hardware supports up to 16 active GPUVMs at any given time.
+ *
+ * Each GPUVM is represented by a 1-2 or 1-5 level page table, depending
+ * on the ASIC family. GPUVM supports RWX attributes on each page as well
+ * as other features such as encryption and caching attributes.
+ *
+ * VMID 0 is special. It is the GPUVM used for the kernel driver. In
+ * addition to an aperture managed by a page table, VMID 0 also has
+ * several other apertures. There is an aperture for direct access to VRAM
+ * and there is a legacy AGP aperture which just forwards accesses directly
+ * to the matching system physical addresses (or IOVAs when an IOMMU is
+ * present). These apertures provide direct access to these memories without
+ * incurring the overhead of a page table. VMID 0 is used by the kernel
+ * driver for tasks like memory management.
+ *
+ * GPU clients (i.e., engines on the GPU) use GPUVM VMIDs to access memory.
+ * For user applications, each application can have their own unique GPUVM
+ * address space. The application manages the address space and the kernel
+ * driver manages the GPUVM page tables for each process. If an GPU client
+ * accesses an invalid page, it will generate a GPU page fault, similar to
+ * accessing an invalid page on a CPU.