[RFC v3 7/8] drm/xe/madvise: Block imported and exported dma-bufs

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

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.

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_vm_madvise.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.c b/drivers/gpu/drm/xe/xe_vm_madvise.c
index 9f2d6c1d3062..868be570664d 100644
--- a/drivers/gpu/drm/xe/xe_vm_madvise.c
+++ b/drivers/gpu/drm/xe/xe_vm_madvise.c
@@ -159,6 +159,31 @@ static void madvise_pat_index(struct xe_device *xe, struct xe_vm *vm,
 	}
 }
 
+/**
+ * xe_bo_is_external_dmabuf() - Check if BO is imported or exported dma-buf
+ * @bo: Buffer object
+ *
+ * Prevent marking imported or exported dma-bufs as purgeable.
+ * External devices may be accessing these buffers without our
+ * knowledge, making purging unsafe.
+ *
+ * Return: true if BO is imported or exported, false otherwise
+ */
+static bool xe_bo_is_external_dmabuf(struct xe_bo *bo)
+{
+	struct drm_gem_object *obj = &bo->ttm.base;
+
+	/* Imported from another driver */
+	if (drm_gem_is_imported(obj))
+		return true;
+
+	/* Exported to another driver */
+	if (obj->dma_buf)
+		return true;
+
+	return false;
+}
+
 /**
  * xe_bo_all_vmas_dontneed() - Check if all VMAs of a BO are marked DONTNEED
  * @bo: Buffer object
@@ -179,6 +204,10 @@ static bool xe_bo_all_vmas_dontneed(struct xe_bo *bo)
 
 	dma_resv_assert_held(bo->ttm.base.resv);
 
+	/* External dma-bufs cannot be purgeable */
+	if (xe_bo_is_external_dmabuf(bo))
+		return false;
+
 	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);
-- 
2.43.0