[RFC PATCH 6/7] tun: populate hash in virtio-net header when needed

[Yuri Benditovich <yuri.benditovich@daynix.com>]

If the BPF program populated the hash in the skb the tun
propagates the hash value and hash report type to the
respective fields of virtio-net header.

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
---
 drivers/net/tun.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 45f4f04a4a3e..214feb0b16fb 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -556,15 +556,20 @@ static u16 tun_ebpf_select_queue(struct tun_struct *tun, struct sk_buff *skb)
 {
 	struct tun_prog *prog;
 	u32 numqueues;
-	u16 ret = 0;
+	u32 ret = 0;
 
 	numqueues = READ_ONCE(tun->numqueues);
 	if (!numqueues)
 		return 0;
 
 	prog = rcu_dereference(tun->steering_prog);
-	if (prog)
+	if (prog) {
 		ret = bpf_prog_run_clear_cb(prog->prog, skb);
+		if (tun->bpf_populates_hash) {
+			*skb_hash_report_type(skb) = (__u8)(ret >> 16);
+			ret &= 0xffff;
+		}
+	}
 
 	return ret % numqueues;
 }
@@ -2062,6 +2067,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
 
 	if (vnet_hdr_sz) {
 		struct virtio_net_hdr gso;
+		__u16 extra_copy = 0;
 
 		if (iov_iter_count(iter) < vnet_hdr_sz)
 			return -EINVAL;
@@ -2085,7 +2091,20 @@ static ssize_t tun_put_user(struct tun_struct *tun,
 		if (copy_to_iter(&gso, sizeof(gso), iter) != sizeof(gso))
 			return -EFAULT;
 
-		iov_iter_advance(iter, vnet_hdr_sz - sizeof(gso));
+		if (tun->bpf_populates_hash &&
+		    vnet_hdr_sz >= sizeof(struct virtio_net_hdr_v1_hash)) {
+			struct virtio_net_hdr_v1_hash hdr;
+
+			hdr.hdr.num_buffers = 0;
+			hdr.hash_value = cpu_to_le32(skb_get_hash(skb));
+			hdr.hash_report = cpu_to_le16(*skb_hash_report_type(skb));
+			hdr.padding = 0;
+			extra_copy = sizeof(hdr) - sizeof(gso);
+			if (copy_to_iter(&hdr.hdr.num_buffers, extra_copy, iter) != extra_copy)
+				return -EFAULT;
+		}
+
+		iov_iter_advance(iter, vnet_hdr_sz - sizeof(gso) - extra_copy);
 	}
 
 	if (vlan_hlen) {
-- 
2.17.1