[PATCH v3 3/7] dma-buf: Document RDMA non-ODP invalidate_mapping() special case

[Leon Romanovsky]

From: Leon Romanovsky <leonro@xxxxxxxxxx>

The .invalidate_mapping() callback is documented as optional, yet it
effectively became mandatory whenever importer_ops were provided. This
led to cases where RDMA non-ODP code had to supply an empty stub just to
provide allow_peer2peer.

Document this behavior by creating a dedicated export for the
dma_buf_unsupported_invalidate_mappings() function. This function is
intended solely for the RDMA non-ODP case and must not be used by any
other dma-buf importer.

This makes it possible to rely on a valid .invalidate_mappings()
callback to determine whether an importer supports revocation.

Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
---
 drivers/dma-buf/dma-buf.c             | 14 ++++++++++++++
 drivers/infiniband/core/umem_dmabuf.c | 11 +----------
 include/linux/dma-buf.h               |  4 +++-
 3 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index cd3b60ce4863..c4fa35034b92 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -1238,6 +1238,20 @@ void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach,
 }
 EXPORT_SYMBOL_NS_GPL(dma_buf_unmap_attachment_unlocked, "DMA_BUF");
 
+/*
+ * This function shouldn't be used by anyone except RDMA non-ODP case.
+ * The reason to it is UAPI mistake where dma-buf was exported to the
+ * userspace without knowing that .invalidate_mappings() can be called
+ * for pinned memory too.
+ *
+ * This warning shouldn't be seen in real production scenario.
+ */
+void dma_buf_unsupported_invalidate_mappings(struct dma_buf_attachment *attach)
+{
+	pr_warn("Invalidate callback should not be called when memory is pinned\n");
+}
+EXPORT_SYMBOL_FOR_MODULES(dma_buf_unsupported_invalidate_mappings, "ib_uverbs");
+
 /**
  * dma_buf_move_notify - notify attachments that DMA-buf is moving
  *
diff --git a/drivers/infiniband/core/umem_dmabuf.c b/drivers/infiniband/core/umem_dmabuf.c
index d77a739cfe7a..81442a887b48 100644
--- a/drivers/infiniband/core/umem_dmabuf.c
+++ b/drivers/infiniband/core/umem_dmabuf.c
@@ -184,18 +184,9 @@ struct ib_umem_dmabuf *ib_umem_dmabuf_get(struct ib_device *device,
 }
 EXPORT_SYMBOL(ib_umem_dmabuf_get);
 
-static void
-ib_umem_dmabuf_unsupported_move_notify(struct dma_buf_attachment *attach)
-{
-	struct ib_umem_dmabuf *umem_dmabuf = attach->importer_priv;
-
-	ibdev_warn_ratelimited(umem_dmabuf->umem.ibdev,
-			       "Invalidate callback should not be called when memory is pinned\n");
-}
-
 static struct dma_buf_attach_ops ib_umem_dmabuf_attach_pinned_ops = {
 	.allow_peer2peer = true,
-	.invalidate_mappings = ib_umem_dmabuf_unsupported_move_notify,
+	.invalidate_mappings = dma_buf_unsupported_invalidate_mappings,
 };
 
 struct ib_umem_dmabuf *
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 1b397635c793..7d7d0a4fb762 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -458,7 +458,7 @@ struct dma_buf_attach_ops {
 	bool allow_peer2peer;
 
 	/**
-	 * @invalidate_mappings: [optional] notification that the DMA-buf is moving
+	 * @invalidate_mappings: notification that the DMA-buf is moving
 	 *
 	 * If this callback is provided the framework can avoid pinning the
 	 * backing store while mappings exists.
@@ -601,6 +601,8 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
 void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
 				enum dma_data_direction);
 void dma_buf_move_notify(struct dma_buf *dma_buf);
+void dma_buf_unsupported_invalidate_mappings(struct dma_buf_attachment *attach);
+
 int dma_buf_begin_cpu_access(struct dma_buf *dma_buf,
 			     enum dma_data_direction dir);
 int dma_buf_end_cpu_access(struct dma_buf *dma_buf,

-- 
2.52.0