[RFC] DRM GPUVA Manager & Nouveau VM_BIND UAPI

This patch series provides a new UAPI for the Nouveau driver in order to support Vulkan features, such as sparse bindings and sparse residency.

Furthermore, with the DRM GPUVA manager it provides a new DRM core feature to keep track of GPU virtual address (VA) mappings in a more generic way.

The DRM GPUVA manager is indented to help drivers implement userspace-manageable GPU VA spaces in reference to the Vulkan API. In order to achieve this goal it serves the following purposes in this context.

1) Provide infrastructure to track GPU VA allocations and mappings,
   making use of the maple_tree.

2) Generically connect GPU VA mappings to their backing buffers, in
   particular DRM GEM objects.

3) Provide a common implementation to perform more complex mapping
   operations on the GPU VA space. In particular splitting and merging
   of GPU VA mappings, e.g. for intersecting mapping requests or partial
   unmap requests.

The new VM_BIND Nouveau UAPI build on top of the DRM GPUVA manager, itself providing the following new interfaces.

1) Initialize a GPU VA space via the new DRM_IOCTL_NOUVEAU_VM_INIT ioctl
   for UMDs to specify the portion of VA space managed by the kernel and
   userspace, respectively.

2) Allocate and free a VA space region as well as bind and unbind memory
   to the GPUs VA space via the new DRM_IOCTL_NOUVEAU_VM_BIND ioctl.

3) Execute push buffers with the new DRM_IOCTL_NOUVEAU_EXEC ioctl.

Both, DRM_IOCTL_NOUVEAU_VM_BIND and DRM_IOCTL_NOUVEAU_EXEC, make use of the DRM scheduler to queue jobs and support asynchronous processing with DRM syncobjs as synchronization mechanism.

By default DRM_IOCTL_NOUVEAU_VM_BIND does synchronous processing, DRM_IOCTL_NOUVEAU_EXEC supports asynchronous processing only.

The new VM_BIND UAPI for Nouveau makes also use of drm_exec (execution context for GEM buffers) by Christian König. Since the patch implementing drm_exec was not yet merged into drm-next it is part of this series, as well as a small fix for this patch, which was found while testing this series.

This patch series is also available at [1].

There is a Mesa NVK merge request by Dave Airlie [2] implementing the corresponding userspace parts for this series.

The Vulkan CTS test suite passes the sparse binding and sparse residency test cases for the new UAPI together with Dave's Mesa work.

There are also some test cases in the igt-gpu-tools project [3] for the new UAPI and hence the DRM GPU VA manager. However, most of them are testing the DRM GPU VA manager's logic through Nouveau's new UAPI and should be considered just as helper for implementation.

However, I absolutely intend to change those test cases to proper kunit test cases for the DRM GPUVA manager, once and if we agree on it's usefulness and design.

[1] https://gitlab.freedesktop.org/nouvelles/kernel/-/tree/new-uapi-drm-next / !1 (closed)

[2] nouveau/mesa!150 (merged)

[3] https://gitlab.freedesktop.org/dakr/igt-gpu-tools/-/tree/wip_nouveau_vm_bind

I also want to give credit to Dave Airlie, who contributed a lot of ideas to this patch series.