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Message-Id: <20241110123532.37831-1-yuezelong@bytedance.com>
Date: Sun, 10 Nov 2024 20:35:32 +0800
From: yuezelong <yuezelong@...edance.com>
To: jgg@...pe.ca,
leon@...nel.org
Cc: linux-rdma@...r.kernel.org,
linux-kernel@...r.kernel.org,
yuezelong <yuezelong@...edance.com>
Subject: [RFC] RDMA/core: Fix IPv6 loopback dst MAC address lookup logic
Imagine we have two RNICs on a single machine, named eth1 and eth2, with
- IPv4 addresses: 192.168.1.2, 192.168.1.3
- IPv6 addresses (scope global): fdbd::beef:2, fdbd::beef:3
- MAC addresses: 11:11:11:11:11:02, 11:11:11:11:11:03,
they all connnected to a gateway with MAC address 22:22:22:22:22:02.
If we want to setup connections between these two RNICs, with RC QP, we
would go through `rdma_resolve_ip` for looking up dst MAC addresses. The
procedure it's the same as using command
`ip route get dst_addr from src_addr oif src_dev`
In IPv4 scenario, you would likely get
```
$ ip route get 192.168.1.2 from 192.168.1.3 oif eth2
192.168.1.2 from 192.168.1.3 via 192.168.1.1 dev eth2 ...
```
Looks reasonable as it would go through the gateway.
But in IPv6 scenario, you would likely get
```
$ ip route get fdbd::beef:2 from fdbd::beef:3 oif eth2
local fdbd::beef:2 from fdbd::beed:3 dev lo table local proto kernel src fdbd::beef:2 metric 0 pref medium
```
This would lead to the RDMA route lookup procedure filling the dst MAC
address with src net device's MAC address (11:11:11:11:11:03), but
filling the dst IP address with dst net device's IPv6 address
(fdbd::beef:2), src net device would drop this packet, and we would fail
to setup the connection.
To make setting up loopback connections like this possible, we need to
send packets to the gateway and let the gateway send it back (actually,
the IPv4 lookup result would lead to this, so there is no problem in IPv4
scenario), so we need to adjust current lookup procedure, if we find out
the src device and dst device is on the same machine (same namespace),
we need to send the packets to the gateway instead of the src device
itself.
Signed-off-by: yuezelong <yuezelong@...edance.com>
---
drivers/infiniband/core/addr.c | 95 +++++++++++++++++++++++++++++++++-
drivers/infiniband/core/cma.c | 7 ++-
2 files changed, 99 insertions(+), 3 deletions(-)
diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
index c4cf26f1d149..d194e6b7f2b9 100644
--- a/drivers/infiniband/core/addr.c
+++ b/drivers/infiniband/core/addr.c
@@ -545,6 +545,29 @@ static void rdma_addr_set_net_defaults(struct rdma_dev_addr *addr)
addr->bound_dev_if = 0;
}
+static struct dst_entry *get_default_ipv6_route(struct in6_addr *src_addr, struct net_device *dev)
+{
+ struct flowi6 fl6;
+ struct dst_entry *dst = NULL;
+
+ memset(&fl6, 0, sizeof(fl6));
+ fl6.flowi6_iif = dev_net(dev)->loopback_dev->ifindex;
+ fl6.flowi6_oif = dev->ifindex;
+ fl6.saddr = *src_addr;
+ fl6.daddr = in6addr_any;
+
+ dst = ipv6_stub->ipv6_dst_lookup_flow(dev_net(dev), NULL, &fl6, NULL);
+ if (IS_ERR(dst))
+ return NULL;
+
+ if (dst && dst->error) {
+ dst_release(dst);
+ return NULL;
+ }
+
+ return dst;
+}
+
static int addr_resolve(struct sockaddr *src_in,
const struct sockaddr *dst_in,
struct rdma_dev_addr *addr,
@@ -597,9 +620,77 @@ static int addr_resolve(struct sockaddr *src_in,
* 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);
+ if (!ret && resolve_neigh) {
+ if ((src_in->sa_family == AF_INET6) && (ndev_flags & IFF_LOOPBACK)) {
+ rcu_read_lock();
+ /*
+ * When src net device and dst net device is different device,
+ * traditional TCP/IP loopback won't work for RDMA. We need to find
+ * gateway for src net device and send packets to the gateway, then
+ * let the gateway send it back to the dst device. This is likely
+ * be problematic in IPv6 scenario, the route logic would likely fill
+ * the dst MAC address with src net device's MAC, but with dst IP
+ * belongs to the dst net device, leading to packet drop.
+ *
+ * Thus, we need to figure out gateway's MAC address in IPv6 loopback
+ * scenario.
+ */
+ struct net_device *ndev = READ_ONCE(dst->dev);
+ struct net_device *src_ndev = rdma_find_ndev_for_src_ip_rcu(dev_net(ndev),
+ src_in);
+ struct net_device *dst_ndev = rdma_find_ndev_for_src_ip_rcu(dev_net(ndev),
+ dst_in);
+
+ if (IS_ERR(src_ndev) || IS_ERR(dst_ndev)) {
+ ret = -ENODEV;
+ rcu_read_unlock();
+ goto exit;
+ }
+
+ if (src_ndev != dst_ndev) {
+ dst_release(dst);
+ dst = get_default_ipv6_route((struct in6_addr *)src_in->sa_data,
+ src_ndev);
+ ndev_flags = src_ndev->flags;
+ } else {
+ rcu_read_unlock();
+ /*
+ * For real loopback (src and dst is the same device), we can
+ * just use the original code path.
+ */
+ ret = addr_resolve_neigh(dst, dst_in, addr, ndev_flags, seq);
+ goto exit;
+ }
+ rcu_read_unlock();
+
+ if (dst == NULL) {
+ ret = -EINVAL;
+ goto done;
+ }
+
+ /*
+ * Though we fill `in6addr_any` as dst addr here, `xfrm_neigh_lookup`
+ * would still find nexthop for us, which provides gateway MAC address.
+ */
+ struct sockaddr_in6 addr_in = {
+ .sin6_family = AF_INET6,
+ .sin6_addr = in6addr_any,
+ };
+ const void *daddr = (const void *)&addr_in.sin6_addr;
+
+ might_sleep();
+
+ /*
+ * Use `addr_resolve_neigh` here would go into `ib_nl_fetch_ha` branch,
+ * which would fail because of `rdma_nl_chk_listeners` returns error.
+ */
+ ret = dst_fetch_ha(dst, addr, daddr);
+ } else {
+ ret = addr_resolve_neigh(dst, dst_in, addr, ndev_flags, seq);
+ }
+ }
+exit:
if (src_in->sa_family == AF_INET)
ip_rt_put(rt);
else
diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
index 64ace0b968f0..744f396568cd 100644
--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -1612,7 +1612,12 @@ static bool validate_ipv6_net_dev(struct net_device *net_dev,
if (!rt)
return false;
- ret = rt->rt6i_idev->dev == net_dev;
+ if (rt->rt6i_flags & (RTF_LOCAL | RTF_NONEXTHOP)) {
+ // TODO: how to validate netdev when the device is loopback?
+ ret = true;
+ } else {
+ ret = rt->rt6i_idev->dev == net_dev;
+ }
ip6_rt_put(rt);
return ret;
--
2.20.1
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