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

Arvind Yadav
2026-03-23T09:31:35Z

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>
---
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.
--
2.43.0