Re: [PATCH v6 17/20] drm/gpusvm: Introduce drm_gpusvm_find_vma_start() function

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

On Wed, Apr 30, 2025 at 05:49:09PM +0530, Himal Prasad Ghimiray wrote:
> The drm_gpusvm_find_vma_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.
> 
> v2
> - Rename function as drm_gpusvm_find_vma_start() (Matthew Brost)
> - mmget/mmput
> 
> Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> ---
>  drivers/gpu/drm/drm_gpusvm.c | 32 ++++++++++++++++++++++++++++++++
>  include/drm/drm_gpusvm.h     |  5 +++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
> index c94a8d7a293d..48bb29b78b96 100644
> --- a/drivers/gpu/drm/drm_gpusvm.c
> +++ b/drivers/gpu/drm/drm_gpusvm.c
> @@ -980,6 +980,38 @@ static void drm_gpusvm_driver_lock_held(struct drm_gpusvm *gpusvm)
>  }
>  #endif
>  
> +/**
> + * drm_gpusvm_find_vma_start() - Find start address for first VMA in 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_find_vma_start(struct drm_gpusvm *gpusvm,
> +			  unsigned long start,
> +			  unsigned long end)
> +{
> +	struct mm_struct *mm = gpusvm->mm;
> +	struct vm_area_struct *vma;
> +	unsigned long addr = ULONG_MAX;
> +
> +	mmget(mm);

The MM could be closed here, so:

if (!mmget_not_zero(mm))
	return addr;

Matt

> +	mmap_read_lock(mm);
> +
> +	vma = find_vma_intersection(mm, start, end);
> +	if (vma)
> +		addr =  vma->vm_start;
> +
> +	mmap_read_unlock(mm);
> +	mmput(mm);
> +
> +	return addr;
> +}
> +EXPORT_SYMBOL_GPL(drm_gpusvm_find_vma_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 eaf704d3d05e..6a5156476bf4 100644
> --- a/include/drm/drm_gpusvm.h
> +++ b/include/drm/drm_gpusvm.h
> @@ -327,6 +327,11 @@ void drm_gpusvm_fini(struct drm_gpusvm *gpusvm);
>  
>  void drm_gpusvm_free(struct drm_gpusvm *gpusvm);
>  
> +unsigned long
> +drm_gpusvm_find_vma_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
>