kernel: 5.4: import wireguard backport

Rather than using the clunky, old, slower wireguard-linux-compat out of
tree module, this commit does a patch-by-patch backport of upstream's
wireguard to 5.4. This specific backport is in widespread use, being
part of SUSE's enterprise kernel, Oracle's enterprise kernel, Google's
Android kernel, Gentoo's distro kernel, and probably more I've forgotten
about. It's definately the "more proper" way of adding wireguard to a
kernel than the ugly compat.h hell of the wireguard-linux-compat repo.
And most importantly for OpenWRT, it allows using the same module
configuration code for 5.10 as for 5.4, with no need for bifurcation.

These patches are from the backport tree which is maintained in the
open here: https://git.zx2c4.com/wireguard-linux/log/?h=backport-5.4.y
I'll be sending PRs to update this as needed.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 58 insertions, 0 deletions

diff --git a/target/linux/generic/backport-5.4/080-wireguard-0100-wireguard-send-receive-cond_resched-when-processing-.patch b/target/linux/generic/backport-5.4/080-wireguard-0100-wireguard-send-receive-cond_resched-when-processing-.patch
new file mode 100644
index 0000000000..a87a383981
--- /dev/null
+++ b/target/linux/generic/backport-5.4/080-wireguard-0100-wireguard-send-receive-cond_resched-when-processing-.patch
@@ -0,0 +1,58 @@
+From 3943211e0997b04f1e2ca1a6624391cc72a176bc Mon Sep 17 00:00:00 2001
+From: "Jason A. Donenfeld" <Jason@zx2c4.com>
+Date: Wed, 6 May 2020 15:33:04 -0600
+Subject: [PATCH 100/124] wireguard: send/receive: cond_resched() when
+ processing worker ringbuffers
+
+commit 4005f5c3c9d006157ba716594e0d70c88a235c5e upstream.
+
+Users with pathological hardware reported CPU stalls on CONFIG_
+PREEMPT_VOLUNTARY=y, because the ringbuffers would stay full, meaning
+these workers would never terminate. That turned out not to be okay on
+systems without forced preemption, which Sultan observed. This commit
+adds a cond_resched() to the bottom of each loop iteration, so that
+these workers don't hog the core. Note that we don't need this on the
+napi poll worker, since that terminates after its budget is expended.
+
+Suggested-by: Sultan Alsawaf <sultan@kerneltoast.com>
+Reported-by: Wang Jian <larkwang@gmail.com>
+Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
+Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
+---
+ drivers/net/wireguard/receive.c | 2 ++
+ drivers/net/wireguard/send.c    | 4 ++++
+ 2 files changed, 6 insertions(+)
+
+--- a/drivers/net/wireguard/receive.c
++++ b/drivers/net/wireguard/receive.c
+@@ -516,6 +516,8 @@ void wg_packet_decrypt_worker(struct wor
+ 				&PACKET_CB(skb)->keypair->receiving)) ?
+ 				PACKET_STATE_CRYPTED : PACKET_STATE_DEAD;
+ 		wg_queue_enqueue_per_peer_napi(skb, state);
++		if (need_resched())
++			cond_resched();
+ 	}
+ }
+ 
+--- a/drivers/net/wireguard/send.c
++++ b/drivers/net/wireguard/send.c
+@@ -281,6 +281,8 @@ void wg_packet_tx_worker(struct work_str
+ 
+ 		wg_noise_keypair_put(keypair, false);
+ 		wg_peer_put(peer);
++		if (need_resched())
++			cond_resched();
+ 	}
+ }
+ 
+@@ -304,6 +306,8 @@ void wg_packet_encrypt_worker(struct wor
+ 		}
+ 		wg_queue_enqueue_per_peer(&PACKET_PEER(first)->tx_queue, first,
+ 					  state);
++		if (need_resched())
++			cond_resched();
+ 	}
+ }
+