[PATCH 2/2] drm/gpuvm: Add locking helpers

[Rob Clark]

On Fri, Jun 13, 2025 at 4:57 PM Rob Clark <robin.clark at oss.qualcomm.com> wrote:
>
> For UNMAP/REMAP steps we could be needing to lock objects that are not
> explicitly listed in the VM_BIND ioctl in order to tear-down unmapped
> VAs.  These helpers handle locking/preparing the needed objects.
>
> Note that these functions do not strictly require the VM changes to be
> applied before the next drm_gpuvm_sm_map_lock()/_unmap_lock() call.  In
> the case that VM changes from an earlier drm_gpuvm_sm_map()/_unmap()
> call result in a differing sequence of steps when the VM changes are
> actually applied, it will be the same set of GEM objects involved, so
> the locking is still correct.
>
> Signed-off-by: Rob Clark <robin.clark at oss.qualcomm.com>

And if it wasn't clear/obvious, the expected usage is something that
looks like: https://gitlab.freedesktop.org/robclark/msm/-/blob/sparse-newer/drivers/gpu/drm/msm/msm_gem_vma.c?ref_type=heads#L1150

ie. the caller handles the drm_exec_until_all_locked bit


BR,
-R

> ---
>  drivers/gpu/drm/drm_gpuvm.c | 81 +++++++++++++++++++++++++++++++++++++
>  include/drm/drm_gpuvm.h     |  8 ++++
>  2 files changed, 89 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
> index 0ca717130541..197066dd390b 100644
> --- a/drivers/gpu/drm/drm_gpuvm.c
> +++ b/drivers/gpu/drm/drm_gpuvm.c
> @@ -2390,6 +2390,87 @@ drm_gpuvm_sm_unmap(struct drm_gpuvm *gpuvm, void *priv,
>  }
>  EXPORT_SYMBOL_GPL(drm_gpuvm_sm_unmap);
>
> +static int
> +drm_gpuva_sm_step_lock(struct drm_gpuva_op *op, void *priv)
> +{
> +       struct drm_exec *exec = priv;
> +
> +       switch (op->op) {
> +       case DRM_GPUVA_OP_REMAP:
> +               if (op->remap.unmap->va->gem.obj)
> +                       return drm_exec_lock_obj(exec, op->remap.unmap->va->gem.obj);
> +               return 0;
> +       case DRM_GPUVA_OP_UNMAP:
> +               if (op->unmap.va->gem.obj)
> +                       return drm_exec_lock_obj(exec, op->unmap.va->gem.obj);
> +               return 0;
> +       default:
> +               return 0;
> +       }
> +}
> +
> +static const struct drm_gpuvm_ops lock_ops = {
> +       .sm_step_map = drm_gpuva_sm_step_lock,
> +       .sm_step_remap = drm_gpuva_sm_step_lock,
> +       .sm_step_unmap = drm_gpuva_sm_step_lock,
> +};
> +
> +/**
> + * drm_gpuvm_sm_map_lock() - locks the objects touched by a drm_gpuvm_sm_map()
> + * @gpuvm: the &drm_gpuvm representing the GPU VA space
> + * @exec: the &drm_exec locking context
> + * @num_fences: for newly mapped objects, the # of fences to reserve
> + * @req_addr: the start address of the range to unmap
> + * @req_range: the range of the mappings to unmap
> + * @req_obj: the &drm_gem_object to map
> + * @req_offset: the offset within the &drm_gem_object
> + *
> + * This function locks (drm_exec_lock_obj()) objects that will be unmapped/
> + * remapped, and locks+prepares (drm_exec_prepare_object()) objects that
> + * will be newly mapped.
> + *
> + * Returns: 0 on success or a negative error code
> + */
> +int
> +drm_gpuvm_sm_map_lock(struct drm_gpuvm *gpuvm,
> +                     struct drm_exec *exec, unsigned int num_fences,
> +                     u64 req_addr, u64 req_range,
> +                     struct drm_gem_object *req_obj, u64 req_offset)
> +{
> +       if (req_obj) {
> +               int ret = drm_exec_prepare_obj(exec, req_obj, num_fences);
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       return __drm_gpuvm_sm_map(gpuvm, &lock_ops, exec,
> +                                 req_addr, req_range,
> +                                 req_obj, req_offset);
> +
> +}
> +EXPORT_SYMBOL_GPL(drm_gpuvm_sm_map_lock);
> +
> +/**
> + * drm_gpuvm_sm_unmap_lock() - locks the objects touched by drm_gpuvm_sm_unmap()
> + * @gpuvm: the &drm_gpuvm representing the GPU VA space
> + * @exec: the &drm_exec locking context
> + * @req_addr: the start address of the range to unmap
> + * @req_range: the range of the mappings to unmap
> + *
> + * This function locks (drm_exec_lock_obj()) objects that will be unmapped/
> + * remapped by drm_gpuvm_sm_unmap().
> + *
> + * Returns: 0 on success or a negative error code
> + */
> +int
> +drm_gpuvm_sm_unmap_lock(struct drm_gpuvm *gpuvm, struct drm_exec *exec,
> +                       u64 req_addr, u64 req_range)
> +{
> +       return __drm_gpuvm_sm_unmap(gpuvm, &lock_ops, exec,
> +                                   req_addr, req_range);
> +}
> +EXPORT_SYMBOL_GPL(drm_gpuvm_sm_unmap_lock);
> +
>  static struct drm_gpuva_op *
>  gpuva_op_alloc(struct drm_gpuvm *gpuvm)
>  {
> diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
> index 0ef837a331d6..a769dccfb3ae 100644
> --- a/include/drm/drm_gpuvm.h
> +++ b/include/drm/drm_gpuvm.h
> @@ -1211,6 +1211,14 @@ int drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm, void *priv,
>  int drm_gpuvm_sm_unmap(struct drm_gpuvm *gpuvm, void *priv,
>                        u64 req_addr, u64 req_range);
>
> +int drm_gpuvm_sm_map_lock(struct drm_gpuvm *gpuvm,
> +                         struct drm_exec *exec, unsigned int num_fences,
> +                         u64 req_addr, u64 req_range,
> +                         struct drm_gem_object *obj, u64 offset);
> +
> +int drm_gpuvm_sm_unmap_lock(struct drm_gpuvm *gpuvm, struct drm_exec *exec,
> +                           u64 req_addr, u64 req_range);
> +
>  void drm_gpuva_map(struct drm_gpuvm *gpuvm,
>                    struct drm_gpuva *va,
>                    struct drm_gpuva_op_map *op);
> --
> 2.49.0
>