net/mlx5e: Trigger neighbor resolution for unresolved destinations

net/mlx5e: Trigger neighbor resolution for unresolved destinations

When initializing the MAC addresses for an outbound IPsec packet offload
rule in mlx5e_ipsec_init_macs, the call to dst_neigh_lookup is used to
find the next-hop neighbor (typically the gateway in tunnel mode).
This call might create a new neighbor entry if one doesn't already
exist. This newly created entry starts in the INCOMPLETE state, as the
kernel hasn't yet sent an ARP or NDISC probe to resolve the MAC
address. In this case, neigh_ha_snapshot will correctly return an
all-zero MAC address.

IPsec packet offload requires the actual next-hop MAC address to
program the rule correctly. If the neighbor state is INCOMPLETE when
the rule is created, the hardware rule is programmed with an all-zero
destination MAC address. Packets sent using this rule will be
subsequently dropped by the receiving network infrastructure or host.

This patch adds a check specifically for the outbound offload path. If
neigh_ha_snapshot returns an all-zero MAC address, it proactively
calls neigh_event_send(n, NULL). This ensures the kernel immediately
sends the initial ARP or NDISC probe if one isn't already pending,
accelerating the resolution process. This helps prevent the hardware
rule from being programmed with an invalid MAC address and avoids
packet drops due to unresolved neighbors.

Fixes: 71670f766b8f ("net/mlx5e: Support routed networks during IPsec MACs initialization")
Signed-off-by: Jianbo Liu <jianbol@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/1765284977-1363052-8-git-send-email-tariqt@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>