Re: [PATCH v7 07/12] drm/xe/madvise: Block imported and exported dma-bufs

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Mon, 2026-03-23 at 15:00 +0530, Arvind Yadav wrote:
> Prevent marking imported or exported dma-bufs as purgeable.
> External devices may be accessing these buffers without our
> knowledge, making purging unsafe.
> 
> Check drm_gem_is_imported() for buffers created by other
> drivers and obj->dma_buf for buffers exported to other
> drivers. Silently skip these BOs during madvise processing.
> 
> This follows drm_gem_shmem's purgeable implementation and
> prevents data corruption from purging actively-used shared
> buffers.
> 
> v3:
>    - Addresses review feedback from Matt Roper about handling
>      imported/exported BOs correctly in the purgeable BO
>      implementation.
> 
> v4:
>    - Check should be add to xe_vm_madvise_purgeable_bo.
> 
> v5:
>    - Rename xe_bo_is_external_dmabuf() to xe_bo_is_dmabuf_shared()
>      for clarity (Thomas)
>    - Update comments to clarify why both imports and exports
>      are unsafe to purge.
> 
> v6:
>   - No PTEs to zap for shared dma-bufs.
> 
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>

Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

> ---
>  drivers/gpu/drm/xe/xe_vm_madvise.c | 38
> ++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.c
> b/drivers/gpu/drm/xe/xe_vm_madvise.c
> index ed1940da7739..340e83764a76 100644
> --- a/drivers/gpu/drm/xe/xe_vm_madvise.c
> +++ b/drivers/gpu/drm/xe/xe_vm_madvise.c
> @@ -185,6 +185,34 @@ static void madvise_pat_index(struct xe_device
> *xe, struct xe_vm *vm,
>  	}
>  }
>  
> +
> +/**
> + * xe_bo_is_dmabuf_shared() - Check if BO is shared via dma-buf
> + * @bo: Buffer object
> + *
> + * Prevent marking imported or exported dma-bufs as purgeable.
> + * For imported BOs, Xe doesn't own the backing store and cannot
> + * safely reclaim pages (exporter or other devices may still be
> + * using them). For exported BOs, external devices may have active
> + * mappings we cannot track.
> + *
> + * Return: true if BO is imported or exported, false otherwise
> + */
> +static bool xe_bo_is_dmabuf_shared(struct xe_bo *bo)
> +{
> +	struct drm_gem_object *obj = &bo->ttm.base;
> +
> +	/* Imported: exporter owns backing store */
> +	if (drm_gem_is_imported(obj))
> +		return true;
> +
> +	/* Exported: external devices may be accessing */
> +	if (obj->dma_buf)
> +		return true;
> +
> +	return false;
> +}
> +
>  /**
>   * enum xe_bo_vmas_purge_state - VMA purgeable state aggregation
>   *
> @@ -234,6 +262,10 @@ static enum xe_bo_vmas_purge_state
> xe_bo_all_vmas_dontneed(struct xe_bo *bo)
>  
>  	xe_bo_assert_held(bo);
>  
> +	/* Shared dma-bufs cannot be purgeable */
> +	if (xe_bo_is_dmabuf_shared(bo))
> +		return XE_BO_VMAS_STATE_WILLNEED;
> +
>  	drm_gem_for_each_gpuvm_bo(vm_bo, obj) {
>  		drm_gpuvm_bo_for_each_va(gpuva, vm_bo) {
>  			struct xe_vma *vma = gpuva_to_vma(gpuva);
> @@ -335,6 +367,12 @@ static void __maybe_unused
> madvise_purgeable(struct xe_device *xe,
>  		/* BO must be locked before modifying madv state */
>  		xe_bo_assert_held(bo);
>  
> +		/* Skip shared dma-bufs - no PTEs to zap */
> +		if (xe_bo_is_dmabuf_shared(bo)) {
> +			vmas[i]->skip_invalidation = true;
> +			continue;
> +		}
> +
>  		/*
>  		 * Once purged, always purged. Cannot transition
> back to WILLNEED.
>  		 * This matches i915 semantics where purged BOs are
> permanently invalid.