[PATCH 02/12] dma-buf: add explicit buffer pinning v2

[Christian König]

Add optional explicit pinning callbacks instead of implicitly assume the
exporter pins the buffer when a mapping is created.

v2: move in patchset and pin the dma-buf in the old mapping code paths.

Signed-off-by: Christian König <christian.koenig at amd.com>
---
 drivers/dma-buf/dma-buf.c | 49 ++++++++++++++++++++++++++++++++++++++-
 include/linux/dma-buf.h   | 38 +++++++++++++++++++++++++-----
 2 files changed, 80 insertions(+), 7 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 50b4c6af04c7..0656dcf289be 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -529,6 +529,41 @@ void dma_buf_put(struct dma_buf *dmabuf)
 }
 EXPORT_SYMBOL_GPL(dma_buf_put);
 
+/**
+ * dma_buf_pin - Lock down the DMA-buf
+ *
+ * @dmabuf:	[in]	DMA-buf to lock down.
+ *
+ * Returns:
+ * 0 on success, negative error code on failure.
+ */
+int dma_buf_pin(struct dma_buf *dmabuf)
+{
+	int ret = 0;
+
+	reservation_object_assert_held(dmabuf->resv);
+
+	if (dmabuf->ops->pin)
+		ret = dmabuf->ops->pin(dmabuf);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dma_buf_pin);
+
+/**
+ * dma_buf_unpin - Remove lock from DMA-buf
+ *
+ * @dmabuf:	[in]	DMA-buf to unlock.
+ */
+void dma_buf_unpin(struct dma_buf *dmabuf)
+{
+	reservation_object_assert_held(dmabuf->resv);
+
+	if (dmabuf->ops->unpin)
+		dmabuf->ops->unpin(dmabuf);
+}
+EXPORT_SYMBOL_GPL(dma_buf_unpin);
+
 /**
  * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
  * calls attach() of dma_buf_ops to allow device-specific attach functionality
@@ -548,7 +583,8 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
  * accessible to @dev, and cannot be moved to a more suitable place. This is
  * indicated with the error code -EBUSY.
  */
-struct dma_buf_attachment *dma_buf_attach(const struct dma_buf_attach_info *info)
+struct dma_buf_attachment *
+dma_buf_attach(const struct dma_buf_attach_info *info)
 {
 	struct dma_buf *dmabuf = info->dmabuf;
 	struct dma_buf_attachment *attach;
@@ -625,12 +661,19 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
 					enum dma_data_direction direction)
 {
 	struct sg_table *sg_table;
+	int r;
 
 	might_sleep();
 
 	if (WARN_ON(!attach || !attach->dmabuf))
 		return ERR_PTR(-EINVAL);
 
+	reservation_object_lock(attach->dmabuf->resv, NULL);
+	r = dma_buf_pin(attach->dmabuf);
+	reservation_object_unlock(attach->dmabuf->resv);
+	if (r)
+		return ERR_PTR(r);
+
 	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
 	if (!sg_table)
 		sg_table = ERR_PTR(-ENOMEM);
@@ -660,6 +703,10 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
 
 	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
 						direction);
+
+	reservation_object_lock(attach->dmabuf->resv, NULL);
+	dma_buf_unpin(attach->dmabuf);
+	reservation_object_unlock(attach->dmabuf->resv);
 }
 EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
 
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 2c312dfd31a1..0321939b1c3d 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -51,6 +51,34 @@ struct dma_buf_attachment;
  * @vunmap: [optional] unmaps a vmap from the buffer
  */
 struct dma_buf_ops {
+	/**
+	 * @pin:
+	 *
+	 * This is called by dma_buf_pin and lets the exporter know that the
+	 * DMA-buf can't be moved any more.
+	 *
+	 * This is called with the dmabuf->resv object locked.
+	 *
+	 * This callback is optional.
+	 *
+	 * Returns:
+	 *
+	 * 0 on success, negative error code on failure.
+	 */
+	int (*pin)(struct dma_buf *);
+
+	/**
+	 * @unpin:
+	 *
+	 * This is called by dma_buf_unpin and lets the exporter know that the
+	 * DMA-buf can be moved again.
+	 *
+	 * This is called with the dmabuf->resv object locked.
+	 *
+	 * This callback is optional.
+	 */
+	void (*unpin)(struct dma_buf *);
+
 	/**
 	 * @attach:
 	 *
@@ -95,9 +123,7 @@ struct dma_buf_ops {
 	 *
 	 * This is called by dma_buf_map_attachment() and is used to map a
 	 * shared &dma_buf into device address space, and it is mandatory. It
-	 * can only be called if @attach has been called successfully. This
-	 * essentially pins the DMA buffer into place, and it cannot be moved
-	 * any more
+	 * can only be called if @attach has been called successfully.
 	 *
 	 * This call may sleep, e.g. when the backing storage first needs to be
 	 * allocated, or moved to a location suitable for all currently attached
@@ -135,9 +161,6 @@ struct dma_buf_ops {
 	 *
 	 * This is called by dma_buf_unmap_attachment() and should unmap and
 	 * release the &sg_table allocated in @map_dma_buf, and it is mandatory.
-	 * It should also unpin the backing storage if this is the last mapping
-	 * of the DMA buffer, it the exporter supports backing storage
-	 * migration.
 	 */
 	void (*unmap_dma_buf)(struct dma_buf_attachment *,
 			      struct sg_table *,
@@ -386,6 +409,9 @@ static inline void get_dma_buf(struct dma_buf *dmabuf)
 	get_file(dmabuf->file);
 }
 
+int dma_buf_pin(struct dma_buf *dmabuf);
+void dma_buf_unpin(struct dma_buf *dmabuf);
+
 struct dma_buf_attachment *
 dma_buf_attach(const struct dma_buf_attach_info *info);
 void dma_buf_detach(struct dma_buf *dmabuf,
-- 
2.17.1