[PATCH net] net: devmem: fix DMA direction on unmapping

[PATCH net] net: devmem: fix DMA direction on unmapping

[Jakub Kicinski]

Looks like we always unmap the DMA_BUF with DMA_FROM_DEVICE direction.
While at it unexport __net_devmem_dmabuf_binding_free(), it's internal.

Found by code inspection.

Fixes: bd61848900bf ("net: devmem: Implement TX path")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
Compile tested only. I could be missing something here.

CC: almasrymina@google.com
CC: asml.silence@gmail.com
CC: sdf@fomichev.me
CC: dw@davidwei.uk
CC: kaiyuanz@google.com
---
 net/core/devmem.h | 7 +++----
 net/core/devmem.c | 6 +++---
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/net/core/devmem.h b/net/core/devmem.h
index 0a3b28ba5c13..41cd6e1c9141 100644
--- a/net/core/devmem.h
+++ b/net/core/devmem.h
@@ -56,6 +56,9 @@ struct net_devmem_dmabuf_binding {
 	 */
 	u32 id;
 
+	/* DMA direction, FROM_DEVICE for Rx binding, TO_DEVICE for Tx. */
+	enum dma_data_direction direction;
+
 	/* Array of net_iov pointers for this binding, sorted by virtual
 	 * address. This array is convenient to map the virtual addresses to
 	 * net_iovs in the TX path.
@@ -165,10 +168,6 @@ static inline void net_devmem_put_net_iov(struct net_iov *niov)
 {
 }
 
-static inline void __net_devmem_dmabuf_binding_free(struct work_struct *wq)
-{
-}
-
 static inline struct net_devmem_dmabuf_binding *
 net_devmem_bind_dmabuf(struct net_device *dev,
 		       enum dma_data_direction direction,
diff --git a/net/core/devmem.c b/net/core/devmem.c
index b3a62ca0df65..24c591ab38ae 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -70,14 +70,13 @@ void __net_devmem_dmabuf_binding_free(struct work_struct *wq)
 		gen_pool_destroy(binding->chunk_pool);
 
 	dma_buf_unmap_attachment_unlocked(binding->attachment, binding->sgt,
-					  DMA_FROM_DEVICE);
+					  binding->direction);
 	dma_buf_detach(binding->dmabuf, binding->attachment);
 	dma_buf_put(binding->dmabuf);
 	xa_destroy(&binding->bound_rxqs);
 	kvfree(binding->tx_vec);
 	kfree(binding);
 }
-EXPORT_SYMBOL(__net_devmem_dmabuf_binding_free);
 
 struct net_iov *
 net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding)
@@ -208,6 +207,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
 	mutex_init(&binding->lock);
 
 	binding->dmabuf = dmabuf;
+	binding->direction = direction;
 
 	binding->attachment = dma_buf_attach(binding->dmabuf, dev->dev.parent);
 	if (IS_ERR(binding->attachment)) {
@@ -312,7 +312,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
 	kvfree(binding->tx_vec);
 err_unmap:
 	dma_buf_unmap_attachment_unlocked(binding->attachment, binding->sgt,
-					  DMA_FROM_DEVICE);
+					  direction);
 err_detach:
 	dma_buf_detach(dmabuf, binding->attachment);
 err_free_binding:
-- 
2.50.1

Re: [PATCH net] net: devmem: fix DMA direction on unmapping

[Stanislav Fomichev]

On 07/31, Jakub Kicinski wrote:
> Looks like we always unmap the DMA_BUF with DMA_FROM_DEVICE direction.
> While at it unexport __net_devmem_dmabuf_binding_free(), it's internal.
> 
> Found by code inspection.
> 
> Fixes: bd61848900bf ("net: devmem: Implement TX path")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> Compile tested only. I could be missing something here.

Acked-by: Stanislav Fomichev <sdf@fomichev.me>

Re: [PATCH net] net: devmem: fix DMA direction on unmapping

[Mina Almasry]

On Thu, Jul 31, 2025 at 6:13 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> Looks like we always unmap the DMA_BUF with DMA_FROM_DEVICE direction.
> While at it unexport __net_devmem_dmabuf_binding_free(), it's internal.
>
> Found by code inspection.
>
> Fixes: bd61848900bf ("net: devmem: Implement TX path")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Thanks!

Reviewed-by: Mina Almasry <almasrymina@google.com>

-- 
Thanks,
Mina

Re: [PATCH net] net: devmem: fix DMA direction on unmapping

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 31 Jul 2025 18:13:35 -0700 you wrote:
> Looks like we always unmap the DMA_BUF with DMA_FROM_DEVICE direction.
> While at it unexport __net_devmem_dmabuf_binding_free(), it's internal.
> 
> Found by code inspection.
> 
> Fixes: bd61848900bf ("net: devmem: Implement TX path")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> 
> [...]

Here is the summary with links:
  - [net] net: devmem: fix DMA direction on unmapping
    https://git.kernel.org/netdev/net/c/fa516c0d8bf9

You are awesome, thank you!
-- 
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