Re: [PATCH RFC 3/3] RDMA/siw: Require non-zero 6-byte MACs for soft iWARP

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, May 31, 2023 at 07:11:52PM +0000, Chuck Lever III wrote:
> 
> 
> > On May 31, 2023, at 3:04 PM, Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > 
> > On Tue, May 23, 2023 at 07:18:18PM +0000, Chuck Lever III wrote:
> > 
> >> The core address resolution code wants to find an L2 address
> >> for the egress device. The underlying ib_device, where a made-up
> >> GID might be stored, is not involved with address resolution
> >> AFAICT.
> > 
> > Where are you hitting this?
> 
>      kworker/2:0-26    [002]   551.962874: funcgraph_entry:                   |  addr_resolve() {
>      kworker/2:0-26    [002]   551.962874: bprint:               addr_resolve: resolve_neigh=true resolve_by_gid_attr=false
>      kworker/2:0-26    [002]   551.962874: funcgraph_entry:                   |    addr4_resolve.constprop.0() {
>      kworker/2:0-26    [002]   551.962875: bprint:               addr4_resolve.constprop.0: src_in=0.0.0.0:35173 dst_in=100.72.1.2:20049
>      kworker/2:0-26    [002]   551.962875: funcgraph_entry:                   |      ip_route_output_flow() {
>      kworker/2:0-26    [002]   551.962875: funcgraph_entry:                   |        ip_route_output_key_hash() {
>      kworker/2:0-26    [002]   551.962876: funcgraph_entry:                   |          ip_route_output_key_hash_rcu() {
>      kworker/2:0-26    [002]   551.962876: funcgraph_entry:        4.526 us   |            __fib_lookup();
>      kworker/2:0-26    [002]   551.962881: funcgraph_entry:        0.264 us   |            fib_select_path();
>      kworker/2:0-26    [002]   551.962881: funcgraph_entry:        1.022 us   |            __mkroute_output();
>      kworker/2:0-26    [002]   551.962882: funcgraph_exit:         6.705 us   |          }
>      kworker/2:0-26    [002]   551.962882: funcgraph_exit:         7.283 us   |        }
>      kworker/2:0-26    [002]   551.962883: funcgraph_exit:         7.624 us   |      }
>      kworker/2:0-26    [002]   551.962883: funcgraph_exit:         8.395 us   |    }
>      kworker/2:0-26    [002]   551.962883: funcgraph_entry:                   |    rdma_set_src_addr_rcu.constprop.0() {
>      kworker/2:0-26    [002]   551.962883: bprint:               rdma_set_src_addr_rcu.constprop.0: ndev=0xffff91f5135a4000 name=tailscale0
>      kworker/2:0-26    [002]   551.962884: funcgraph_entry:                   |      copy_src_l2_addr() {
>      kworker/2:0-26    [002]   551.962884: funcgraph_entry:        0.984 us   |        iff_flags2string();
>      kworker/2:0-26    [002]   551.962885: bprint:               copy_src_l2_addr: ndev=0xffff91f5135a4000 dst_in=100.72.1.2:20049 flags=UP|POINTOPOINT|NOARP|MULTICAST
>      kworker/2:0-26    [002]   551.962885: funcgraph_entry:                   |        rdma_copy_src_l2_addr() {
>      kworker/2:0-26    [002]   551.962886: funcgraph_entry:        0.148 us   |          devtype2string();
>      kworker/2:0-26    [002]   551.962887: bprint:               rdma_copy_src_l2_addr: name=tailscale0 type=NONE src_dev_addr=00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 broadcast=00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ifindex=3
>      kworker/2:0-26    [002]   551.962887: funcgraph_exit:         1.488 us   |        }
>      kworker/2:0-26    [002]   551.962887: bprint:               copy_src_l2_addr: network type=IB
>      kworker/2:0-26    [002]   551.962887: funcgraph_exit:         3.636 us   |      }
>      kworker/2:0-26    [002]   551.962887: funcgraph_exit:         4.275 us   |    }
> 
> 
> Address resolution finds the right device, but there's
> a zero-value L2 address.

Sure, but why is that a problem?

This got to rdma_set_src_addr_rcu, so the resolution suceeded, where
is the failure? From the above trace I think addr_resolve() succeeded?

> Thus it cannot form a unique GID from that. Perhaps there needs to
> be a call to query_gid in here?

So your issue is cma_iw_acquire_dev() which looks like it is encoding
the MAC into the GID for some reason? We don't do that on rocee, the
GID encodes the IP address

I have no idea how iWarp works, but this is surprising that it puts a
MAC in the GID..

If the iwarp device has only one GID ever and it is always the "MAC"
the cma_iw_acquire_dev()'s logic is simply wrong, it should check that
the dev_addr's netdev matches the one and only GID and just use the
GID. No reason to search for GIDs.

A small edit to cma_validate_port() might make sense, it is kind of
wrong to force the gid_type to IB_GID_TYPE_IB for whatever ARPHRD type
the tunnel is using.

Jason