drm/amdgpu: expand on GPUVM documentation (4670ac70) · Commits · EulixOS / Software / Kernel

drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c

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		/**
		* DOC: GPUVM
		*
		* GPUVM is similar to the legacy gart on older asics, however
		* rather than there being a single global gart table
		* for the entire GPU, there are multiple VM page tables active
		* at any given time. The VM page tables can contain a mix
		* vram pages and system memory pages and system memory pages
		* GPUVM is the MMU functionality provided on the GPU.
		* GPUVM is similar to the legacy GART on older asics, however
		* rather than there being a single global GART table
		* for the entire GPU, there can be multiple GPUVM page tables active
		* at any given time. The GPUVM page tables can contain a mix
		* VRAM pages and system pages (both memory and MMIO) and system pages
		* can be mapped as snooped (cached system pages) or unsnooped
		* (uncached system pages).
		* Each VM has an ID associated with it and there is a page table
		* associated with each VMID. When executing a command buffer,
		* the kernel tells the ring what VMID to use for that command
		*
		* Each active GPUVM has an ID associated with it and there is a page table
		* linked with each VMID. When executing a command buffer,
		* the kernel tells the engine what VMID to use for that command
		* buffer. VMIDs are allocated dynamically as commands are submitted.
		* The userspace drivers maintain their own address space and the kernel
		* sets up their pages tables accordingly when they submit their
		* command buffers and a VMID is assigned.
		* Cayman/Trinity support up to 8 active VMs at any given time;
		* SI supports 16.
		* 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.
		*/

		#define START(node) ((node)->start)