[PATCH 4.20 33/80] virtio_net: Differentiate sk_buff and xdp_frame on freeing

Greg Kroah-Hartman
2019-02-04T10:52:44Z

From: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>

[ Upstream commit 5050471d35d1316ba32dfcbb409978337eb9e75e

I had to fold commit df133f3f9625 ("virtio_net: bulk free tx skbs")
into this to make it work. ]

We do not reset or free up unused buffers when enabling/disabling XDP,
so it can happen that xdp_frames are freed after disabling XDP or
sk_buffs are freed after enabling XDP on xdp tx queues.
Thus we need to handle both forms (xdp_frames and sk_buffs) regardless
of XDP setting.
One way to trigger this problem is to disable XDP when napi_tx is
enabled. In that case, virtnet_xdp_set() calls virtnet_napi_enable()
which kicks NAPI. The NAPI handler will call virtnet_poll_cleantx()
which invokes free_old_xmit_skbs() for queues which have been used by
XDP.

Note that even with this change we need to keep skipping
free_old_xmit_skbs() from NAPI handlers when XDP is enabled, because XDP
tx queues do not aquire queue locks.

- v2: Use napi_consume_skb() instead of dev_consume_skb_any()

Fixes: 4941d472bf95 ("virtio-net: do not reset during XDP set")
Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/virtio_net.c | 64 ++++++++++++++++++++++++++++++++++-------------
1 file changed, 47 insertions(+), 17 deletions(-)

--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -57,6 +57,8 @@ module_param(napi_tx, bool, 0644);
#define VIRTIO_XDP_TX BIT(0)
#define VIRTIO_XDP_REDIR BIT(1)

+#define VIRTIO_XDP_FLAG BIT(0)
+
/* RX packet size EWMA. The average packet size is used to determine the packet
* buffer size when refilling RX rings. As the entire RX ring may be refilled
* at once, the weight is chosen so that the EWMA will be insensitive to short-
@@ -251,6 +253,21 @@ struct padded_vnet_hdr {
char padding[4];
};

+static bool is_xdp_frame(void *ptr)
+{
+ return (unsigned long)ptr & VIRTIO_XDP_FLAG;
+}
+
+static void *xdp_to_ptr(struct xdp_frame *ptr)
+{
+ return (void *)((unsigned long)ptr | VIRTIO_XDP_FLAG);
+}
+
+static struct xdp_frame *ptr_to_xdp(void *ptr)
+{
+ return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
+}
+
/* Converting between virtqueue no. and kernel tx/rx queue no.
* 0:rx0 1:tx0 2:rx1 3:tx1 ... 2N:rxN 2N+1:txN 2N+2:cvq
*/
@@ -461,7 +478,8 @@ static int __virtnet_xdp_xmit_one(struct

sg_init_one(sq->sg, xdpf->data, xdpf->len);

- err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdpf, GFP_ATOMIC);
+ err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdp_to_ptr(xdpf),
+ GFP_ATOMIC);
if (unlikely(err))
return -ENOSPC; /* Caller handle free/refcnt */

@@ -481,13 +499,13 @@ static int virtnet_xdp_xmit(struct net_d
{
struct virtnet_info *vi = netdev_priv(dev);
struct receive_queue *rq = vi->rq;
- struct xdp_frame *xdpf_sent;
struct bpf_prog *xdp_prog;
struct send_queue *sq;
unsigned int len;
int drops = 0;
int kicks = 0;
int ret, err;
+ void *ptr;
int i;

/* Only allow ndo_xdp_xmit if XDP is loaded on dev, as this
@@ -506,8 +524,12 @@ static int virtnet_xdp_xmit(struct net_d
}

/* Free up any pending old buffers before queueing new ones. */
- while ((xdpf_sent = virtqueue_get_buf(sq->vq, &len)) != NULL)
- xdp_return_frame(xdpf_sent);
+ while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
+ if (likely(is_xdp_frame(ptr)))
+ xdp_return_frame(ptr_to_xdp(ptr));
+ else
+ napi_consume_skb(ptr, false);
+ }

for (i = 0; i < n; i++) {
struct xdp_frame *xdpf = frames[i];
@@ -1326,20 +1348,28 @@ static int virtnet_receive(struct receiv
return stats.packets;
}

-static void free_old_xmit_skbs(struct send_queue *sq)
+static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
{
- struct sk_buff *skb;
unsigned int len;
unsigned int packets = 0;
unsigned int bytes = 0;
+ void *ptr;

- while ((skb = virtqueue_get_buf(sq->vq, &len)) != NULL) {
- pr_debug("Sent skb %p\n", skb);
+ while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
+ if (likely(!is_xdp_frame(ptr))) {
+ struct sk_buff *skb = ptr;

- bytes += skb->len;
- packets++;
+ pr_debug("Sent skb %p\n", skb);

- dev_consume_skb_any(skb);
+ bytes += skb->len;
+ napi_consume_skb(skb, in_napi);
+ } else {
+ struct xdp_frame *frame = ptr_to_xdp(ptr);
+
+ bytes += frame->len;
+ xdp_return_frame(frame);
+ }
+ packets++;
}

/* Avoid overhead when no packets have been processed
@@ -1375,7 +1405,7 @@ static void virtnet_poll_cleantx(struct
return;

if (__netif_tx_trylock(txq)) {
- free_old_xmit_skbs(sq);
+ free_old_xmit_skbs(sq, true);
__netif_tx_unlock(txq);
}

@@ -1459,7 +1489,7 @@ static int virtnet_poll_tx(struct napi_s

txq = netdev_get_tx_queue(vi->dev, index);
__netif_tx_lock(txq, raw_smp_processor_id());
- free_old_xmit_skbs(sq);
+ free_old_xmit_skbs(sq, true);
__netif_tx_unlock(txq);

virtqueue_napi_complete(napi, sq->vq, 0);
@@ -1528,7 +1558,7 @@ static netdev_tx_t start_xmit(struct sk_
bool use_napi = sq->napi.weight;

/* Free up any pending old buffers before queueing new ones. */
- free_old_xmit_skbs(sq);
+ free_old_xmit_skbs(sq, false);

if (use_napi && kick)
virtqueue_enable_cb_delayed(sq->vq);
@@ -1571,7 +1601,7 @@ static netdev_tx_t start_xmit(struct sk_
if (!use_napi &&
unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
/* More just got used, free them then recheck. */
- free_old_xmit_skbs(sq);
+ free_old_xmit_skbs(sq, false);
if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
netif_start_subqueue(dev, qnum);
virtqueue_disable_cb(sq->vq);
@@ -2639,10 +2669,10 @@ static void free_unused_bufs(struct virt
for (i = 0; i < vi->max_queue_pairs; i++) {
struct virtqueue *vq = vi->sq[i].vq;
while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) {
- if (!is_xdp_raw_buffer_queue(vi, i))
+ if (!is_xdp_frame(buf))
dev_kfree_skb(buf);
else
- xdp_return_frame(buf);
+ xdp_return_frame(ptr_to_xdp(buf));
}
}