linux-kernel - [PATCH 3/4] RDMA/core: Use route entry flag to decide on loopback traffic

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Message-ID: <20250907160833.56589-4-edwards@nvidia.com>
Date: Sun, 7 Sep 2025 19:08:32 +0300
From: Edward Srouji <edwards@...dia.com>
To: <jgg@...pe.ca>, <leon@...nel.org>
CC: <linux-rdma@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<parav@...dia.com>, <cratiu@...dia.com>, <vdumitrescu@...dia.com>,
	<edwards@...dia.com>, <kuba@...nel.org>, <tariqt@...dia.com>,
	<mbloch@...dia.com>, <gal@...dia.com>
Subject: [PATCH 3/4] RDMA/core: Use route entry flag to decide on loopback traffic

From: Parav Pandit <parav@...dia.com>

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@...dia.com>
Reviewed-by: Vlad Dumitrescu <vdumitrescu@...dia.com>
Signed-off-by: Edward Srouji <edwards@...dia.com>
---
 drivers/infiniband/core/addr.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
index ca86c482662f..61596cda2b65 100644
--- a/drivers/infiniband/core/addr.c
+++ b/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;
 
@@ -575,7 +583,7 @@ 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();
 
 	/*
@@ -583,7 +591,7 @@ static int addr_resolve(struct sockaddr *src_in,
 	 * 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);
-- 
2.21.3