net/af_xdp: forbid umem sharing for xsks with same context

AF_XDP PMDs who wish to share a UMEM must have a unique context
(ctx) ie. netdev,qid tuple. For instance, the following will not
work since both PMDs' contexts are identical.

  --vdev net_af_xdp0,iface=ens786f1,start_queue=0,shared_umem=1
  --vdev net_af_xdp1,iface=ens786f1,start_queue=0,shared_umem=1

Supporting this scenario would require locks, which would impact
the performance of the more typical cases - xsks with different
netdev,qid tuples.

Fixes: 74b46340e2d4 ("net/af_xdp: support shared UMEM")

Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>

diff --git a/doc/guides/nics/af_xdp.rst b/doc/guides/nics/af_xdp.rst
index be268fe..052e59a 100644 (file)
--- a/doc/guides/nics/af_xdp.rst
+++ b/doc/guides/nics/af_xdp.rst
@@ -82,3 +82,28 @@ Limitations
 
   Note: The AF_XDP PMD will fail to initialise if an MTU which violates the driver's
   conditions as above is set prior to launching the application.
+
+- **Shared UMEM**
+
+  The sharing of UMEM is only supported for AF_XDP sockets with unique contexts.
+  The context refers to the netdev,qid tuple.
+
+  The following combination will fail:
+
+  .. code-block:: console
+
+    --vdev net_af_xdp0,iface=ens786f1,shared_umem=1 \
+    --vdev net_af_xdp1,iface=ens786f1,shared_umem=1 \
+
+  Either of the following however is permitted since either the netdev or qid differs
+  between the two vdevs:
+
+  .. code-block:: console
+
+    --vdev net_af_xdp0,iface=ens786f1,shared_umem=1 \
+    --vdev net_af_xdp1,iface=ens786f1,start_queue=1,shared_umem=1 \
+
+  .. code-block:: console
+
+    --vdev net_af_xdp0,iface=ens786f1,shared_umem=1 \
+    --vdev net_af_xdp1,iface=ens786f2,shared_umem=1 \
\ No newline at end of file

diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c b/drivers/net/af_xdp/rte_eth_af_xdp.c
index ac00cba..0562e58 100644 (file)
--- a/drivers/net/af_xdp/rte_eth_af_xdp.c
+++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
@@ -634,16 +634,35 @@ find_internal_resource(struct pmd_internals *port_int)
        return list;
 }
 
+/* Check if the netdev,qid context already exists */
+static inline bool
+ctx_exists(struct pkt_rx_queue *rxq, const char *ifname,
+               struct pkt_rx_queue *list_rxq, const char *list_ifname)
+{
+       bool exists = false;
+
+       if (rxq->xsk_queue_idx == list_rxq->xsk_queue_idx &&
+                       !strncmp(ifname, list_ifname, IFNAMSIZ)) {
+               AF_XDP_LOG(ERR, "ctx %s,%i already exists, cannot share umem\n",
+                                       ifname, rxq->xsk_queue_idx);
+               exists = true;
+       }
+
+       return exists;
+}
+
 /* Get a pointer to an existing UMEM which overlays the rxq's mb_pool */
-static inline struct xsk_umem_info *
-get_shared_umem(struct pkt_rx_queue *rxq) {
+static inline int
+get_shared_umem(struct pkt_rx_queue *rxq, const char *ifname,
+                       struct xsk_umem_info **umem)
+{
        struct internal_list *list;
        struct pmd_internals *internals;
-       int i = 0;
+       int i = 0, ret = 0;
        struct rte_mempool *mb_pool = rxq->mb_pool;
 
        if (mb_pool == NULL)
-               return NULL;
+               return ret;
 
        pthread_mutex_lock(&internal_list_lock);
 
@@ -655,20 +674,25 @@ get_shared_umem(struct pkt_rx_queue *rxq) {
                        if (rxq == list_rxq)
                                continue;
                        if (mb_pool == internals->rx_queues[i].mb_pool) {
+                               if (ctx_exists(rxq, ifname, list_rxq,
+                                               internals->if_name)) {
+                                       ret = -1;
+                                       goto out;
+                               }
                                if (__atomic_load_n(
                                        &internals->rx_queues[i].umem->refcnt,
                                                        __ATOMIC_ACQUIRE)) {
-                                       pthread_mutex_unlock(
-                                                       &internal_list_lock);
-                                       return internals->rx_queues[i].umem;
+                                       *umem = internals->rx_queues[i].umem;
+                                       goto out;
                                }
                        }
                }
        }
 
+out:
        pthread_mutex_unlock(&internal_list_lock);
 
-       return NULL;
+       return ret;
 }
 
 static int
@@ -913,7 +937,9 @@ xsk_umem_info *xdp_umem_configure(struct pmd_internals *internals,
        uint64_t umem_size, align = 0;
 
        if (internals->shared_umem) {
-               umem = get_shared_umem(rxq);
+               if (get_shared_umem(rxq, internals->if_name, &umem) < 0)
+                       return NULL;
+
                if (umem != NULL &&
                        __atomic_load_n(&umem->refcnt, __ATOMIC_ACQUIRE) <
                                        umem->max_xsks) {