[PATCH net-next v9 07/14] net: Proxy netdev_queue_get_dma_dev for leased queues

[Daniel Borkmann <daniel@iogearbox.net>]

From: David Wei <dw@davidwei.uk>

Extend netdev_queue_get_dma_dev to return the physical device of the
real rxq for DMA in case the queue was leased. This allows memory
providers like io_uring zero-copy or devmem to bind to the physically
leased rxq via virtual devices such as netkit.

Signed-off-by: David Wei <dw@davidwei.uk>
Co-developed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 include/net/netdev_queues.h |  3 ++-
 net/core/netdev_queues.c    | 36 ++++++++++++++++++++++++++++--------
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/include/net/netdev_queues.h b/include/net/netdev_queues.h
index 567bc2efde6d..260558192ab1 100644
--- a/include/net/netdev_queues.h
+++ b/include/net/netdev_queues.h
@@ -380,7 +380,8 @@ static inline unsigned int netif_xmit_timeout_ms(struct netdev_queue *txq)
 					 get_desc, start_thrs);		\
 	})
 
-struct device *netdev_queue_get_dma_dev(struct net_device *dev, int idx);
+struct device *netdev_queue_get_dma_dev(struct net_device *dev,
+					unsigned int idx);
 bool netdev_can_create_queue(const struct net_device *dev,
 			     struct netlink_ext_ack *extack);
 bool netdev_can_lease_queue(const struct net_device *dev,
diff --git a/net/core/netdev_queues.c b/net/core/netdev_queues.c
index 92a0b6b2842f..437e9cd0cc7a 100644
--- a/net/core/netdev_queues.c
+++ b/net/core/netdev_queues.c
@@ -6,27 +6,47 @@
 
 #include "dev.h"
 
+static struct device *
+__netdev_queue_get_dma_dev(struct net_device *dev, unsigned int idx)
+{
+	const struct netdev_queue_mgmt_ops *queue_ops = dev->queue_mgmt_ops;
+	struct device *dma_dev;
+
+	if (queue_ops && queue_ops->ndo_queue_get_dma_dev)
+		dma_dev = queue_ops->ndo_queue_get_dma_dev(dev, idx);
+	else
+		dma_dev = dev->dev.parent;
+
+	return dma_dev && dma_dev->dma_mask ? dma_dev : NULL;
+}
+
 /**
  * netdev_queue_get_dma_dev() - get dma device for zero-copy operations
  * @dev:	net_device
  * @idx:	queue index
  *
- * Get dma device for zero-copy operations to be used for this queue.
+ * Get dma device for zero-copy operations to be used for this queue. If the
+ * queue is leased from a physical queue, we retrieve the physical queue's
+ * dma device.
  * When such device is not available or valid, the function will return NULL.
  *
  * Return: Device or NULL on error
  */
-struct device *netdev_queue_get_dma_dev(struct net_device *dev, int idx)
+struct device *netdev_queue_get_dma_dev(struct net_device *dev,
+					unsigned int idx)
 {
-	const struct netdev_queue_mgmt_ops *queue_ops = dev->queue_mgmt_ops;
+	struct net_device *orig_dev = dev;
 	struct device *dma_dev;
 
-	if (queue_ops && queue_ops->ndo_queue_get_dma_dev)
-		dma_dev = queue_ops->ndo_queue_get_dma_dev(dev, idx);
-	else
-		dma_dev = dev->dev.parent;
+	if (!netif_rxq_is_leased(dev, idx))
+		return __netdev_queue_get_dma_dev(dev, idx);
 
-	return dma_dev && dma_dev->dma_mask ? dma_dev : NULL;
+	if (!netif_get_rx_queue_lease_locked(&dev, &idx))
+		return NULL;
+
+	dma_dev = __netdev_queue_get_dma_dev(dev, idx);
+	netif_put_rx_queue_lease_locked(orig_dev, dev);
+	return dma_dev;
 }
 
 bool netdev_can_create_queue(const struct net_device *dev,
-- 
2.43.0