RDMA/core: Use route entry flag to decide on loopback traffic

addr_resolve() considers a destination to be local if the next-hop
device of the resolved route for the destination is the loopback
netdevice.

This fails when the source and destination IP addresses belong to
a netdev enslaved to a VRF netdev. In this case the next-hop device
is the VRF itself:

 $ ip link add name myvrf up type vrf table 100
 $ ip link set ens2f0np0 master myvrf up
 $ ip addr add 192.168.1.1/24 dev ens2f0np0
 $ ip route get 192.168.1.1 oif myvrf
 local 192.168.1.1 dev myvrf table 100 src 192.168.1.1 uid 0
    cache <local>

This results in packets being generated with an incorrect destination
MAC of the VRF netdevice and ib_write_bw failing with timeout.

Solve this by determining if a destination is local or not based on
the resolved route's type rather than based on its next-hop netdevice
loopback flag.

This enables to resolve loopback traffic with and without VRF
configurations in a uniform way.

Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Vlad Dumitrescu <vdumitrescu@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
Link: https://patch.msgid.link/20250916111103.84069-4-edwards@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>

Author: paravmellanox

drivers/infiniband/core/addr.c

@@ -446,31 +446,40 @@ static int addr6_resolve(struct sockaddr *src_sock,
 }
 #endif
 
+static bool is_dst_local(const struct dst_entry *dst)
+{
+	if (dst->ops->family == AF_INET)
+		return !!(dst_rtable(dst)->rt_type & RTN_LOCAL);
+	else if (dst->ops->family == AF_INET6)
+		return !!(dst_rt6_info(dst)->rt6i_flags & RTF_LOCAL);
+	else
+		return false;
+}
+
 static int addr_resolve_neigh(const struct dst_entry *dst,
 			      const struct sockaddr *dst_in,
 			      struct rdma_dev_addr *addr,
-			      unsigned int ndev_flags,
 			      u32 seq)
 {
-	int ret = 0;
-
-	if (ndev_flags & IFF_LOOPBACK)
+	if (is_dst_local(dst)) {
+		/* When the destination is local entry, source and destination
+		 * are same. Skip the neighbour lookup.
+		 */
 		memcpy(addr->dst_dev_addr, addr->src_dev_addr, MAX_ADDR_LEN);
-	else
-		ret = fetch_ha(dst, addr, dst_in, seq);
-	return ret;
+		return 0;
+	}
+
+	return fetch_ha(dst, addr, dst_in, seq);
 }
 
 static int rdma_set_src_addr_rcu(struct rdma_dev_addr *dev_addr,
-				 unsigned int *ndev_flags,
 				 const struct sockaddr *dst_in,
 				 const struct dst_entry *dst)
 {
 	struct net_device *ndev = READ_ONCE(dst->dev);
 
-	*ndev_flags = ndev->flags;
 	/* A physical device must be the RDMA device to use */
-	if (ndev->flags & IFF_LOOPBACK) {
+	if (is_dst_local(dst)) {
 		int ret;
 		/*
 		 * RDMA (IB/RoCE, iWarp) doesn't run on lo interface or
@@ -538,7 +547,6 @@ static int addr_resolve(struct sockaddr *src_in,
 			u32 seq)
 {
 	struct dst_entry *dst = NULL;
-	unsigned int ndev_flags = 0;
 	struct rtable *rt = NULL;
 	int ret;
 
@@ -575,15 +583,15 @@ static int addr_resolve(struct sockaddr *src_in,
 		rcu_read_unlock();
 		goto done;
 	}
-	ret = rdma_set_src_addr_rcu(addr, &ndev_flags, dst_in, dst);
+	ret = rdma_set_src_addr_rcu(addr, dst_in, dst);
 	rcu_read_unlock();
 
 	/*
 	 * Resolve neighbor destination address if requested and
 	 * only if src addr translation didn't fail.
 	 */
 	if (!ret && resolve_neigh)
-		ret = addr_resolve_neigh(dst, dst_in, addr, ndev_flags, seq);
+		ret = addr_resolve_neigh(dst, dst_in, addr, seq);
 
 	if (src_in->sa_family == AF_INET)
 		ip_rt_put(rt);