Re: [PATCH v5 17/20] drm/gpusvm: Introduce drm_gpusvm_range_find_or_insert_start() function

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Apr 29, 2025 at 04:12:30PM +0530, Himal Prasad Ghimiray wrote:
> The drm_gpusvm_range_find_or_insert_start() function is used to
> determine the starting address of a CPU VMA within a specified user
> range. If the range does not contain any VMA, the function returns
> ULONG_MAX.
> 
> Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> ---
>  drivers/gpu/drm/drm_gpusvm.c | 29 +++++++++++++++++++++++++++++
>  include/drm/drm_gpusvm.h     |  5 +++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
> index 40a56f38ff8e..bb7c589b8d15 100644
> --- a/drivers/gpu/drm/drm_gpusvm.c
> +++ b/drivers/gpu/drm/drm_gpusvm.c
> @@ -980,6 +980,35 @@ static void drm_gpusvm_driver_lock_held(struct drm_gpusvm *gpusvm)
>  }
>  #endif
>  
> +/**
> + * drm_gpusvm_range_find_or_insert_start() - Find or insert start address for range
> + * @gpusvm: Pointer to the GPU SVM structure
> + * @start: The inclusive start user address.
> + * @end: The exclusive end user address.
> + *
> + * Returns: The start address of first VMA within the provided range,
> + * ULONG_MAX otherwise. Assumes start_addr < end_addr.
> + */
> +unsigned long
> +drm_gpusvm_range_find_or_insert_start(struct drm_gpusvm *gpusvm,
> +				      unsigned long start,
> +				      unsigned long end)

We don't really do an insertion here, so maybe:

s/drm_gpusvm_range_find_or_insert_start/drm_gpusvm_find_vma_start

> +{
> +	struct mm_struct *mm = gpusvm->mm;
> +	struct vm_area_struct *vma;
> +	unsigned long addr = ULONG_MAX;
> +

Hmm, do you think we need a mmget here? I'd expect this be called from a
user context where we'd have a MM ref but maybe to be safe add a
mmget/put?

Matt 

> +	mmap_read_lock(mm);
> +
> +	vma = find_vma_intersection(mm, start, end);
> +	if (vma)
> +		addr =  vma->vm_start;
> +
> +	mmap_read_unlock(mm);
> +	return addr;
> +}
> +EXPORT_SYMBOL_GPL(drm_gpusvm_range_find_or_insert_start);
> +
>  /**
>   * drm_gpusvm_range_find_or_insert() - Find or insert GPU SVM range
>   * @gpusvm: Pointer to the GPU SVM structure
> diff --git a/include/drm/drm_gpusvm.h b/include/drm/drm_gpusvm.h
> index cce217bc136f..b0e9ee5c6226 100644
> --- a/include/drm/drm_gpusvm.h
> +++ b/include/drm/drm_gpusvm.h
> @@ -315,6 +315,11 @@ void drm_gpusvm_fini(struct drm_gpusvm *gpusvm);
>  
>  void drm_gpusvm_free(struct drm_gpusvm *gpusvm);
>  
> +unsigned long
> +drm_gpusvm_range_find_or_insert_start(struct drm_gpusvm *gpusvm,
> +				      unsigned long start,
> +				      unsigned long end);
> +
>  struct drm_gpusvm_range *
>  drm_gpusvm_range_find_or_insert(struct drm_gpusvm *gpusvm,
>  				unsigned long fault_addr,
> -- 
> 2.34.1
>