[PATCH net-next 09/10] net: devmem: add netdev_has_dmabuf_binding() helper

[Tariq Toukan]

From: Dragos Tatulea <dtatulea@xxxxxxxxxx>

Currently there is no way to check whether a dmabuf is bound on a TX
queue. RX side has netif_rxq_has_unreadable_mp() which gives a hint
of it.

To help with that, add a helper to check whether a devmem dmabuf
binding may still be in use on a given netdev, optionally filtered by
the DMA device the dmabuf was mapped against.

A binding can outlive its xarray slot: it can still be referenced by
in-flight TX skbs, whose DMA mappings are only valid for the device the
dmabuf was attached to. Reporting such a binding as gone would let a
driver swap the DMA device out from under those skbs. For this reason,
track bindings for their whole lifetime on a new list.

This API is necessary for the upcoming support of data direct in mlx5e.

Signed-off-by: Dragos Tatulea <dtatulea@xxxxxxxxxx>
Cc: Bobby Eshleman <bobbyeshleman@xxxxxxxxx>
Signed-off-by: Tariq Toukan <tariqt@xxxxxxxxxx>
---
 include/net/netmem.h | 23 +++++++++++++++++++++++
 net/core/devmem.c    | 30 ++++++++++++++++++++++++++++++
 net/core/devmem.h    |  2 ++
 3 files changed, 55 insertions(+)

diff --git a/include/net/netmem.h b/include/net/netmem.h
index 0cc8572f62ca..8bcf44f43d17 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -387,16 +387,39 @@ static inline unsigned long netmem_get_dma_addr(netmem_ref netmem)
 	return netmem_to_nmdesc(netmem)->dma_addr;
 }
 
+struct net_device;
+
 #if defined(CONFIG_NET_DEVMEM)
 static inline bool net_is_devmem_iov(const struct net_iov *niov)
 {
 	return niov->type == NET_IOV_DMABUF;
 }
+
+/**
+ * netdev_has_dmabuf_binding - is there a dmabuf binding for a
+ * given @dev and @dma_dev
+ *
+ * @dev: netdev to check bindings
+ * @dma_dev: dma device to check, when NULL it will not be checked
+ *
+ * A binding is reported until its last reference is dropped, which can be
+ * long after the user unbound it: net_iovs of a TX binding can still be
+ * queued in flight, with DMA mappings that are only valid for @dma_dev.
+ *
+ * Return: true if a binding is found under @dev and possibly @dma_dev
+ */
+bool netdev_has_dmabuf_binding(struct net_device *dev, struct device *dma_dev);
 #else
 static inline bool net_is_devmem_iov(const struct net_iov *niov)
 {
 	return false;
 }
+
+static inline bool netdev_has_dmabuf_binding(struct net_device *dev,
+					     struct device *dma_dev)
+{
+	return false;
+}
 #endif
 
 void __get_netmem(netmem_ref netmem);
diff --git a/net/core/devmem.c b/net/core/devmem.c
index 07c62e2e3088..173d66d1cb6e 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -25,6 +25,9 @@
 
 static DEFINE_XARRAY_FLAGS(net_devmem_dmabuf_bindings, XA_FLAGS_ALLOC1);
 
+static DEFINE_SPINLOCK(net_devmem_live_bindings_lock);
+static LIST_HEAD(net_devmem_live_bindings);
+
 static const struct memory_provider_ops dmabuf_devmem_ops;
 
 static struct net_iov *net_iov_free_pop(struct net_iov_area *area,
@@ -63,6 +66,10 @@ void __net_devmem_dmabuf_binding_free(struct work_struct *wq)
 {
 	struct net_devmem_dmabuf_binding *binding = container_of(wq, typeof(*binding), unbind_w);
 
+	spin_lock(&net_devmem_live_bindings_lock);
+	list_del(&binding->live_list);
+	spin_unlock(&net_devmem_live_bindings_lock);
+
 	if (binding->freelist)
 		WARN(binding->free_count != binding->area.num_niovs,
 		     "destroying dmabuf binding with outstanding net_iovs: total=%zu, free=%u",
@@ -321,6 +328,10 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
 
 	list_add(&binding->list, &priv->bindings);
 
+	spin_lock(&net_devmem_live_bindings_lock);
+	list_add(&binding->live_list, &net_devmem_live_bindings);
+	spin_unlock(&net_devmem_live_bindings_lock);
+
 	return binding;
 
 err_free_niovs:
@@ -357,6 +368,25 @@ struct net_devmem_dmabuf_binding *net_devmem_lookup_dmabuf(u32 id)
 	return binding;
 }
 
+bool netdev_has_dmabuf_binding(struct net_device *dev, struct device *dma_dev)
+{
+	struct net_devmem_dmabuf_binding *binding;
+	bool found = false;
+
+	spin_lock(&net_devmem_live_bindings_lock);
+	list_for_each_entry(binding, &net_devmem_live_bindings, live_list) {
+		if (dev == READ_ONCE(binding->dev) &&
+		    (!dma_dev || binding->attachment->dev == dma_dev)) {
+			found = true;
+			break;
+		}
+	}
+	spin_unlock(&net_devmem_live_bindings_lock);
+
+	return found;
+}
+EXPORT_SYMBOL_GPL(netdev_has_dmabuf_binding);
+
 void net_devmem_get_net_iov(struct net_iov *niov)
 {
 	net_devmem_dmabuf_binding_get(net_devmem_iov_binding(niov));
diff --git a/net/core/devmem.h b/net/core/devmem.h
index 1cec10f0257c..eadf6df38687 100644
--- a/net/core/devmem.h
+++ b/net/core/devmem.h
@@ -54,6 +54,8 @@ struct net_devmem_dmabuf_binding {
 	 */
 	struct list_head list;
 
+	struct list_head live_list;
+
 	/* rxq's this binding is active on. */
 	struct xarray bound_rxqs;
 
-- 
2.44.0