tuntap: add missing xdp flush

Web:        https://git.kernel.org/torvalds/c/762c330d670e3d4b795cf7a8d761866fdd1eef49
Commit:     762c330d670e3d4b795cf7a8d761866fdd1eef49
Parent:     cb9f7a9a5c96a773bbc9c70660dc600cfff82f82
Refname:    refs/heads/master
Author:     Jason Wang <[email protected]>
AuthorDate: Wed Feb 7 17:14:46 2018 +0800
Committer:  David S. Miller <[email protected]>
CommitDate: Thu Feb 8 14:10:30 2018 -0500

    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 <[email protected]>
    Signed-off-by: David S. Miller <[email protected]>
---
 drivers/net/tun.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

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;
 }
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