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

[Arvind Yadav <arvind.yadav@intel.com>]

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>
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