Re: [PATCH v8 09/12] drm/xe/dma_buf: Block export of DONTNEED/purged BOs

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

On Thu, Mar 26, 2026 at 11:21:08AM +0530, Arvind Yadav wrote:
> Don't allow exporting BOs marked DONTNEED or PURGED as dma-bufs.
> DONTNEED BOs can have their contents discarded at any time, making
> the exported dma-buf unusable for external devices. PURGED BOs have
> no backing store and are permanently invalid.
> 
> Return -EBUSY for DONTNEED BOs (temporary purgeable state) and
> -EINVAL for purged BOs (permanent, no backing store).
> 
> The export path now checks the BO's purgeable state before creating
> the dma-buf, preventing external devices from accessing memory that
> may be purged at any time.
> 
> v6:
> - Split DONTNEED → -EBUSY and PURGED → -EINVAL for consistency
>   with the rest of the series (Thomas, Matt)
> 
> v7:
> - Use Interruptible lock. (Thomas)
> 
> v8:
> - Check xe_bo_lock() return value and propagate error. (Thomas)
> 
> Cc: Matthew Brost <matthew.brost@intel.com>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_dma_buf.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_dma_buf.c b/drivers/gpu/drm/xe/xe_dma_buf.c
> index ea370cd373e9..7f9602b3363d 100644
> --- a/drivers/gpu/drm/xe/xe_dma_buf.c
> +++ b/drivers/gpu/drm/xe/xe_dma_buf.c
> @@ -223,6 +223,26 @@ struct dma_buf *xe_gem_prime_export(struct drm_gem_object *obj, int flags)
>  	if (bo->vm)
>  		return ERR_PTR(-EPERM);
>  
> +	/*
> +	 * Reject exporting purgeable BOs. DONTNEED BOs can be purged
> +	 * at any time, making the exported dma-buf unusable. Purged BOs
> +	 * have no backing store and are permanently invalid.
> +	 */
> +	ret = xe_bo_lock(bo, true);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	if (xe_bo_madv_is_dontneed(bo)) {
> +		ret = -EBUSY;
> +		goto out_unlock;
> +	}
> +
> +	if (xe_bo_is_purged(bo)) {
> +		ret = -EINVAL;
> +		goto out_unlock;
> +	}
> +	xe_bo_unlock(bo);
> +
>  	ret = ttm_bo_setup_export(&bo->ttm, &ctx);
>  	if (ret)
>  		return ERR_PTR(ret);
> @@ -232,6 +252,10 @@ struct dma_buf *xe_gem_prime_export(struct drm_gem_object *obj, int flags)
>  		buf->ops = &xe_dmabuf_ops;
>  
>  	return buf;
> +
> +out_unlock:
> +	xe_bo_unlock(bo);
> +	return ERR_PTR(ret);
>  }
>  
>  static struct drm_gem_object *
> -- 
> 2.43.0
>