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drm/amdgpu: expand on GPUVM documentation

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Expand the GPUVM documentation to better describe the
hardware functionality and use cases it serves.

v2: Fixed a couple of spelling mistakes.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://lore.kernel.org/r/20221201214153.8453-2-alexander.deucher@amd.com
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
This commit is contained in:
Alex Deucher 2022-12-01 16:41:53 -05:00
parent 57f019864b
commit 4670ac706f
1 changed files with 31 additions and 10 deletions
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41
drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
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@ -45,22 +45,43 @@
/**
* 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)