[PATCH] drm/gem-shmem: Pin and unpin buffers when importing w/o S/G table - Linaro-mm-sig

14 Aug 2025

Imported dma-buf objects need to be pinned while being vmap'ed into
kernel address space. This used to be done before while creating an
S/G table.
GEM-SHMEN can import dma-buf objects without creating the S/G table,
but the pin/unpin is now missing. Leads to page-mapping errors such
as the one shown below.
[  102.101726] BUG: unable to handle page fault for address: ffffc90127000000
[...]
[  102.157102] RIP: 0010:udl_compress_hline16+0x219/0x940 [udl]
[...]
[  102.243250] Call Trace:
[  102.245695]  <TASK>
[  102.2477V95]  ? validate_chain+0x24e/0x5e0
[  102.251805]  ? __lock_acquire+0x568/0xae0
[  102.255807]  udl_render_hline+0x165/0x341 [udl]
[  102.260338]  ? __pfx_udl_render_hline+0x10/0x10 [udl]
[  102.265379]  ? local_clock_noinstr+0xb/0x100
[  102.269642]  ? __lock_release.isra.0+0x16c/0x2e0
[  102.274246]  ? mark_held_locks+0x40/0x70
[  102.278177]  udl_primary_plane_helper_atomic_update+0x43e/0x680 [udl]
[  102.284606]  ? __pfx_udl_primary_plane_helper_atomic_update+0x10/0x10 [udl]
[  102.291551]  ? lockdep_hardirqs_on_prepare.part.0+0x92/0x170
[  102.297208]  ? lockdep_hardirqs_on+0x88/0x130
[  102.301554]  ? _raw_spin_unlock_irq+0x24/0x50
[  102.305901]  ? wait_for_completion_timeout+0x2bb/0x3a0
[  102.311028]  ? drm_atomic_helper_calc_timestamping_constants+0x141/0x200
[  102.317714]  ? drm_atomic_helper_commit_planes+0x3b6/0x1030
[  102.323279]  drm_atomic_helper_commit_planes+0x3b6/0x1030
[  102.328664]  drm_atomic_helper_commit_tail+0x41/0xb0
[  102.333622]  commit_tail+0x204/0x330
[...]
[  102.529946] ---[ end trace 0000000000000000 ]---
[  102.651980] RIP: 0010:udl_compress_hline16+0x219/0x940 [udl]
Support pin/unpin in drm_buf_map_attachment() without creating an S/G
table. Passing DMA_NONE for the DMA direction will only pin. Do the
inverse for unmap_attachment(). Modify GEM-SHMEM accordingly, so that
it pins the imported dma-buf.
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de
Fixes: 660cd44659a0 ("drm/shmem-helper: Import dmabuf without mapping its sg_table")
Reported-by: Thomas Zimmermann tzimmermann@suse.de
Closes: https://lore.kernel.org/dri-devel/ba1bdfb8-dbf7-4372-bdcb-df7e0511c702@suse....
Cc: Shixiong Ou oushixiong@kylinos.cn
Cc: Thomas Zimmermann tzimmermann@suse.de
Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com
Cc: Maxime Ripard mripard@kernel.org
Cc: David Airlie airlied@gmail.com
Cc: Simona Vetter simona@ffwll.ch
Cc: Sumit Semwal sumit.semwal@linaro.org
Cc: "Christian König" christian.koenig@amd.com
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
---
 drivers/dma-buf/dma-buf.c              | 16 +++++++++++++---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 11 ++++++++++-
 drivers/gpu/drm/drm_prime.c            |  2 ++
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 2bcf9ceca997..f1e1385ce630 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -1086,7 +1086,8 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_unpin, "DMA_BUF");
  * @direction:	[in]	direction of DMA transfer
  *
  * Returns sg_table containing the scatterlist to be returned; returns ERR_PTR
- * on error. May return -EINTR if it is interrupted by a signal.
+ * on error. May return -EINTR if it is interrupted by a signal. Returns NULL
+ * on success iff direction is DMA_NONE.
  *
  * On success, the DMA addresses and lengths in the returned scatterlist are
  * PAGE_SIZE aligned.
@@ -1122,6 +1123,8 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
    	if (ret)
    		return ERR_PTR(ret);
    }
+	if (!valid_dma_direction(direction))
+		return NULL; /* only pin; don't map */
sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
    if (!sg_table)
@@ -1216,14 +1219,21 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
 {
    might_sleep();
-	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
+	if (WARN_ON(!attach || !attach->dmabuf))
    	return;
dma_resv_assert_held(attach->dmabuf->resv);
+	if (!valid_dma_direction(direction))
+		goto unpin;
+
+	if (WARN_ON(!sg_table))
+		return;
+
    mangle_sg_table(sg_table);
    attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
+unpin:
    if (dma_buf_pin_on_map(attach))
    	attach->dmabuf->ops->unpin(attach);
 }
@@ -1245,7 +1255,7 @@ void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach,
 {
    might_sleep();
-	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
+	if (WARN_ON(!attach || !attach->dmabuf))
    	return;
dma_resv_lock(attach->dmabuf->resv, NULL);
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 5d1349c34afd..1b66501420d3 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -817,6 +817,7 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
    						 struct dma_buf *dma_buf)
 {
    struct dma_buf_attachment *attach;
+	struct sg_table *sgt;
    struct drm_gem_shmem_object *shmem;
    struct drm_gem_object *obj;
    size_t size;
@@ -838,12 +839,18 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
get_dma_buf(dma_buf);
+	sgt = dma_buf_map_attachment_unlocked(attach, DMA_NONE);
+	if (IS_ERR(sgt)) {
+		ret = PTR_ERR(sgt);
+		goto fail_detach;
+	}
+
    size = PAGE_ALIGN(attach->dmabuf->size);
shmem = __drm_gem_shmem_create(dev, size, true, NULL);
    if (IS_ERR(shmem)) {
    	ret = PTR_ERR(shmem);
-		goto fail_detach;
+		goto fail_unmap;
    }
drm_dbg_prime(dev, "size = %zu\n", size);
@@ -853,6 +860,8 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
return &shmem->base;
+fail_unmap:
+	dma_buf_unmap_attachment_unlocked(attach, sgt, DMA_NONE);
 fail_detach:
    dma_buf_detach(dma_buf, attach);
    dma_buf_put(dma_buf);
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 43a10b4af43a..b3b070868e3b 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -1109,6 +1109,8 @@ void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *sg)
    attach = obj->import_attach;
    if (sg)
    	dma_buf_unmap_attachment_unlocked(attach, sg, DMA_BIDIRECTIONAL);
+	else
+		dma_buf_unmap_attachment_unlocked(attach, NULL, DMA_NONE);
    dma_buf = attach->dmabuf;
    dma_buf_detach(attach->dmabuf, attach);
    /* remove the reference */
-- 
2.50.1


    