tuntap: add missing xdp flush

When using devmap to redirect packets between interfaces,
xdp_do_flush() is usually a must to flush any batched
packets. Unfortunately this is missed in current tuntap
implementation.

Unlike most hardware driver which did XDP inside NAPI loop and call
xdp_do_flush() at then end of each round of poll. TAP did it in the
context of process e.g tun_get_user(). So fix this by count the
pending redirected packets and flush when it exceeds NAPI_POLL_WEIGHT
or MSG_MORE was cleared by sendmsg() caller.

With this fix, xdp_redirect_map works again between two TAPs.

Fixes: 761876c857cb ("tap: XDP support")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 0 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 0dc66e4fbb2c..17e496b88f81 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -181,6 +181,7 @@ struct tun_file {
         struct tun_struct *detached;
         struct ptr_ring tx_ring;
         struct xdp_rxq_info xdp_rxq;
+        int xdp_pending_pkts;
 };
 
 struct tun_flow_entry {
@@ -1665,6 +1666,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
                 case XDP_REDIRECT:
                         get_page(alloc_frag->page);
                         alloc_frag->offset += buflen;
+                        ++tfile->xdp_pending_pkts;
                         err = xdp_do_redirect(tun->dev, &xdp, xdp_prog);
                         if (err)
                                 goto err_redirect;
@@ -1986,6 +1988,11 @@ static ssize_t tun_chr_write_iter(struct kiocb *iocb, struct iov_iter *from)
         result = tun_get_user(tun, tfile, NULL, from,
                               file->f_flags & O_NONBLOCK, false);
 
+        if (tfile->xdp_pending_pkts) {
+                tfile->xdp_pending_pkts = 0;
+                xdp_do_flush_map();
+        }
+
         tun_put(tun);
         return result;
 }
@@ -2322,6 +2329,13 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
         ret = tun_get_user(tun, tfile, m->msg_control, &m->msg_iter,
                            m->msg_flags & MSG_DONTWAIT,
                            m->msg_flags & MSG_MORE);
+
+        if (tfile->xdp_pending_pkts >= NAPI_POLL_WEIGHT ||
+            !(m->msg_flags & MSG_MORE)) {
+                tfile->xdp_pending_pkts = 0;
+                xdp_do_flush_map();
+        }
+
         tun_put(tun);
         return ret;
 }
@@ -3153,6 +3167,7 @@ static int tun_chr_open(struct inode *inode, struct file * file)
         sock_set_flag(&tfile->sk, SOCK_ZEROCOPY);
 
         memset(&tfile->tx_ring, 0, sizeof(tfile->tx_ring));
+        tfile->xdp_pending_pkts = 0;
 
         return 0;
 }