Linux Virtualization - Dec 2016 - [PATCH net 3/9] virtio-net: fix page miscount during XDP linearizing

Merry Xmas and a Happy New year to all:

This series tries to fixes several issues for virtio-net XDP which
could be categorized into several parts:

- fix several issues during XDP linearizing
- allow csumed packet to work for XDP_PASS
- make EWMA rxbuf size estimation works for XDP
- forbid XDP when GUEST_UFO is support
- remove big packet XDP support
- add XDP support or small buffer

Please see individual patches for details.

Thanks

Jason Wang (9):
  virtio-net: remove the warning before XDP linearizing
  virtio-net: correctly xmit linearized page on XDP_TX
  virtio-net: fix page miscount during XDP linearizing
  virtio-net: correctly handle XDP_PASS for linearized packets
  virtio-net: unbreak csumed packets for XDP_PASS
  virtio-net: make rx buf size estimation works for XDP
  virtio-net: forbid XDP when VIRTIO_NET_F_GUEST_UFO is support
  virtio-net: remove big packet XDP codes
  virtio-net: XDP support for small buffers

 drivers/net/virtio_net.c | 172 ++++++++++++++++++++++++++++-------------------
 1 file changed, 102 insertions(+), 70 deletions(-)

-- 
2.7.4

Since we use EWMA to estimate the size of rx buffer. When rx buffer
size is underestimated, it's usual to have a packet with more than one
buffers. Consider this is not a bug, remove the warning and correct
the comment before XDP linearizing.

Cc: John Fastabend <john.r.fastabend at intel.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 08327e0..1067253 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -552,14 +552,8 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 		struct page *xdp_page;
 		u32 act;
 
-		/* No known backend devices should send packets with
-		 * more than a single buffer when XDP conditions are
-		 * met. However it is not strictly illegal so the case
-		 * is handled as an exception and a warning is thrown.
-		 */
+		/* This happens when rx buffer size is underestimated */
 		if (unlikely(num_buf > 1)) {
-			bpf_warn_invalid_xdp_buffer();
-
 			/* linearize data for XDP */
 			xdp_page = xdp_linearize_page(rq, num_buf,
 						      page, offset, &len);
-- 
2.7.4

After we linearize page, we should xmit this page instead of the page
of first buffer which may lead unexpected result. With this patch, we
can see correct packet during XDP_TX.

Cc: John Fastabend <john.r.fastabend at intel.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 1067253..fe4562d 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -572,7 +572,7 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
 			goto err_xdp;
 
-		act = do_xdp_prog(vi, rq, xdp_prog, page, offset, len);
+		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
 		switch (act) {
 		case XDP_PASS:
 			if (unlikely(xdp_page != page))
-- 
2.7.4

We don't put page during linearizing, the would cause leaking when
xmit through XDP_TX or the packet exceeds PAGE_SIZE. Fix them by
put page accordingly. Also decrease the number of buffers during
linearizing to make sure caller can free buffers correctly when packet
exceeds PAGE_SIZE. With this patch, we won't get OOM after linearize
huge number of packets.

Cc: John Fastabend <john.r.fastabend at intel.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index fe4562d..58ad40e 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -483,7 +483,7 @@ static struct sk_buff *receive_big(struct net_device *dev,
  * anymore.
  */
 static struct page *xdp_linearize_page(struct receive_queue *rq,
-				       u16 num_buf,
+				       u16 *num_buf,
 				       struct page *p,
 				       int offset,
 				       unsigned int *len)
@@ -497,7 +497,7 @@ static struct page *xdp_linearize_page(struct receive_queue
*rq,
 	memcpy(page_address(page) + page_off, page_address(p) + offset, *len);
 	page_off += *len;
 
-	while (--num_buf) {
+	while (--*num_buf) {
 		unsigned int buflen;
 		unsigned long ctx;
 		void *buf;
@@ -507,19 +507,22 @@ static struct page *xdp_linearize_page(struct
receive_queue *rq,
 		if (unlikely(!ctx))
 			goto err_buf;
 
+		buf = mergeable_ctx_to_buf_address(ctx);
+		p = virt_to_head_page(buf);
+		off = buf - page_address(p);
+
 		/* guard against a misconfigured or uncooperative backend that
 		 * is sending packet larger than the MTU.
 		 */
-		if ((page_off + buflen) > PAGE_SIZE)
+		if ((page_off + buflen) > PAGE_SIZE) {
+			put_page(p);
 			goto err_buf;
-
-		buf = mergeable_ctx_to_buf_address(ctx);
-		p = virt_to_head_page(buf);
-		off = buf - page_address(p);
+		}
 
 		memcpy(page_address(page) + page_off,
 		       page_address(p) + off, buflen);
 		page_off += buflen;
+		put_page(p);
 	}
 
 	*len = page_off;
@@ -555,7 +558,7 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 		/* This happens when rx buffer size is underestimated */
 		if (unlikely(num_buf > 1)) {
 			/* linearize data for XDP */
-			xdp_page = xdp_linearize_page(rq, num_buf,
+			xdp_page = xdp_linearize_page(rq, &num_buf,
 						      page, offset, &len);
 			if (!xdp_page)
 				goto err_xdp;
-- 
2.7.4

When XDP_PASS were determined for linearized packets, we try to get
new buffers in the virtqueue and build skbs from them. This is wrong,
we should create skbs based on existed buffers instead. Fixing them by
creating skb based on xdp_page.

With this patch "ping 192.168.100.4 -s 3900 -M do" works for XDP_PASS.

Cc: John Fastabend <john.r.fastabend at intel.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 58ad40e..470293e 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -578,8 +578,14 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
 		switch (act) {
 		case XDP_PASS:
-			if (unlikely(xdp_page != page))
-				__free_pages(xdp_page, 0);
+			/* We can only create skb based on xdp_page. */
+			if (unlikely(xdp_page != page)) {
+				rcu_read_unlock();
+				put_page(page);
+				head_skb = page_to_skb(vi, rq, xdp_page,
+						       0, len, PAGE_SIZE);
+				return head_skb;
+			}
 			break;
 		case XDP_TX:
 			if (unlikely(xdp_page != page))
-- 
2.7.4

We drop csumed packet when do XDP for packets. This breaks
XDP_PASS when GUEST_CSUM is supported. Fix this by allowing csum flag
to be set. With this patch, simple TCP works for XDP_PASS.

Cc: John Fastabend <john.r.fastabend at intel.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 470293e..0778dc8 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -440,7 +440,7 @@ static struct sk_buff *receive_big(struct net_device *dev,
 		struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
 		u32 act;
 
-		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
+		if (unlikely(hdr->hdr.gso_type))
 			goto err_xdp;
 		act = do_xdp_prog(vi, rq, xdp_prog, page, 0, len);
 		switch (act) {
@@ -572,7 +572,7 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 		 * the receive path after XDP is loaded. In practice I
 		 * was not able to create this condition.
 		 */
-		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
+		if (unlikely(hdr->hdr.gso_type))
 			goto err_xdp;
 
 		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
-- 
2.7.4

We don't update ewma rx buf size in the case of XDP. This will lead
underestimation of rx buf size which causes host to produce more than
one buffers. This will greatly increase the possibility of XDP page
linearization.

Cc: John Fastabend <john.r.fastabend at intel.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0778dc8..77ae358 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -584,10 +584,12 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 				put_page(page);
 				head_skb = page_to_skb(vi, rq, xdp_page,
 						       0, len, PAGE_SIZE);
+				ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
 				return head_skb;
 			}
 			break;
 		case XDP_TX:
+			ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
 			if (unlikely(xdp_page != page))
 				goto err_xdp;
 			rcu_read_unlock();
@@ -596,6 +598,7 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 		default:
 			if (unlikely(xdp_page != page))
 				__free_pages(xdp_page, 0);
+			ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
 			goto err_xdp;
 		}
 	}
-- 
2.7.4

When VIRTIO_NET_F_GUEST_UFO is negotiated, host could still send UFO
packet that exceeds a single page which could not be handled
correctly by XDP. So this patch forbids setting XDP when GUEST_UFO is
supported. While at it, forbid XDP for ECN (which comes only from GRO)
too to prevent user from misconfiguration.

Cc: John Fastabend <john.r.fastabend at intel.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 77ae358..c1f66d8 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1684,7 +1684,9 @@ static int virtnet_xdp_set(struct net_device *dev, struct
bpf_prog *prog)
 	int i, err;
 
 	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
-	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6)) {
+	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
+	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
+	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO)) {
 		netdev_warn(dev, "can't set XDP while host is implementing LRO,
disable LRO first\n");
 		return -EOPNOTSUPP;
 	}
-- 
2.7.4

Now we in fact don't allow XDP for big packets, remove its codes.

Cc: John Fastabend <john.r.fastabend at intel.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 44 +++-----------------------------------------
 1 file changed, 3 insertions(+), 41 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c1f66d8..e53365a8 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -344,11 +344,7 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
 	/* Free up any pending old buffers before queueing new ones. */
 	while ((xdp_sent = virtqueue_get_buf(sq->vq, &len)) != NULL) {
 		struct page *sent_page = virt_to_head_page(xdp_sent);
-
-		if (vi->mergeable_rx_bufs)
-			put_page(sent_page);
-		else
-			give_pages(rq, sent_page);
+		put_page(sent_page);
 	}
 
 	/* Zero header and leave csum up to XDP layers */
@@ -360,15 +356,8 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
 	err = virtqueue_add_outbuf(sq->vq, sq->sg, num_sg,
 				   xdp->data, GFP_ATOMIC);
 	if (unlikely(err)) {
-		if (vi->mergeable_rx_bufs)
-			put_page(page);
-		else
-			give_pages(rq, page);
+		put_page(page);
 		return; // On error abort to avoid unnecessary kick
-	} else if (!vi->mergeable_rx_bufs) {
-		/* If not mergeable bufs must be big packets so cleanup pages */
-		give_pages(rq, (struct page *)page->private);
-		page->private = 0;
 	}
 
 	virtqueue_kick(sq->vq);
@@ -430,44 +419,17 @@ static struct sk_buff *receive_big(struct net_device *dev,
 				   void *buf,
 				   unsigned int len)
 {
-	struct bpf_prog *xdp_prog;
 	struct page *page = buf;
-	struct sk_buff *skb;
-
-	rcu_read_lock();
-	xdp_prog = rcu_dereference(rq->xdp_prog);
-	if (xdp_prog) {
-		struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
-		u32 act;
-
-		if (unlikely(hdr->hdr.gso_type))
-			goto err_xdp;
-		act = do_xdp_prog(vi, rq, xdp_prog, page, 0, len);
-		switch (act) {
-		case XDP_PASS:
-			break;
-		case XDP_TX:
-			rcu_read_unlock();
-			goto xdp_xmit;
-		case XDP_DROP:
-		default:
-			goto err_xdp;
-		}
-	}
-	rcu_read_unlock();
+	struct sk_buff *skb = page_to_skb(vi, rq, page, 0, len, PAGE_SIZE);
 
-	skb = page_to_skb(vi, rq, page, 0, len, PAGE_SIZE);
 	if (unlikely(!skb))
 		goto err;
 
 	return skb;
 
-err_xdp:
-	rcu_read_unlock();
 err:
 	dev->stats.rx_dropped++;
 	give_pages(rq, page);
-xdp_xmit:
 	return NULL;
 }
 
-- 
2.7.4

Commit f600b6905015 ("virtio_net: Add XDP support") leaves the case of
small receive buffer untouched. This will confuse the user who want to
set XDP but use small buffers. Other than forbid XDP in small buffer
mode, let's make it work. XDP then can only work at skb->data since
virtio-net create skbs during refill, this is sub optimal which could
be optimized in the future.

Cc: John Fastabend <john.r.fastabend at intel.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 112 ++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 87 insertions(+), 25 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index e53365a8..5deeda6 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -333,9 +333,9 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 static void virtnet_xdp_xmit(struct virtnet_info *vi,
 			     struct receive_queue *rq,
 			     struct send_queue *sq,
-			     struct xdp_buff *xdp)
+			     struct xdp_buff *xdp,
+			     void *data)
 {
-	struct page *page = virt_to_head_page(xdp->data);
 	struct virtio_net_hdr_mrg_rxbuf *hdr;
 	unsigned int num_sg, len;
 	void *xdp_sent;
@@ -343,20 +343,45 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
 
 	/* Free up any pending old buffers before queueing new ones. */
 	while ((xdp_sent = virtqueue_get_buf(sq->vq, &len)) != NULL) {
-		struct page *sent_page = virt_to_head_page(xdp_sent);
-		put_page(sent_page);
+		if (vi->mergeable_rx_bufs) {
+			struct page *sent_page = virt_to_head_page(xdp_sent);
+
+			put_page(sent_page);
+		} else { /* small buffer */
+			struct sk_buff *skb = xdp_sent;
+
+			kfree_skb(skb);
+		}
 	}
 
-	/* Zero header and leave csum up to XDP layers */
-	hdr = xdp->data;
-	memset(hdr, 0, vi->hdr_len);
+	if (vi->mergeable_rx_bufs) {
+		/* Zero header and leave csum up to XDP layers */
+		hdr = xdp->data;
+		memset(hdr, 0, vi->hdr_len);
+
+		num_sg = 1;
+		sg_init_one(sq->sg, xdp->data, xdp->data_end - xdp->data);
+	} else { /* small buffer */
+		struct sk_buff *skb = data;
 
-	num_sg = 1;
-	sg_init_one(sq->sg, xdp->data, xdp->data_end - xdp->data);
+		/* Zero header and leave csum up to XDP layers */
+		hdr = skb_vnet_hdr(skb);
+		memset(hdr, 0, vi->hdr_len);
+
+		num_sg = 2;
+		sg_init_table(sq->sg, 2);
+		sg_set_buf(sq->sg, hdr, vi->hdr_len);
+		skb_to_sgvec(skb, sq->sg + 1, 0, skb->len);
+	}
 	err = virtqueue_add_outbuf(sq->vq, sq->sg, num_sg,
-				   xdp->data, GFP_ATOMIC);
+				   data, GFP_ATOMIC);
 	if (unlikely(err)) {
-		put_page(page);
+		if (vi->mergeable_rx_bufs) {
+			struct page *page = virt_to_head_page(xdp->data);
+
+			put_page(page);
+		} else /* small buffer */
+			kfree_skb(data);
 		return; // On error abort to avoid unnecessary kick
 	}
 
@@ -366,23 +391,26 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
 static u32 do_xdp_prog(struct virtnet_info *vi,
 		       struct receive_queue *rq,
 		       struct bpf_prog *xdp_prog,
-		       struct page *page, int offset, int len)
+		       void *data, int len)
 {
 	int hdr_padded_len;
 	struct xdp_buff xdp;
+	void *buf;
 	unsigned int qp;
 	u32 act;
-	u8 *buf;
-
-	buf = page_address(page) + offset;
 
-	if (vi->mergeable_rx_bufs)
+	if (vi->mergeable_rx_bufs) {
 		hdr_padded_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
-	else
-		hdr_padded_len = sizeof(struct padded_vnet_hdr);
+		xdp.data = data + hdr_padded_len;
+		xdp.data_end = xdp.data + (len - vi->hdr_len);
+		buf = data;
+	} else { /* small buffers */
+		struct sk_buff *skb = data;
 
-	xdp.data = buf + hdr_padded_len;
-	xdp.data_end = xdp.data + (len - vi->hdr_len);
+		xdp.data = skb->data;
+		xdp.data_end = xdp.data + len;
+		buf = skb->data;
+	}
 
 	act = bpf_prog_run_xdp(xdp_prog, &xdp);
 	switch (act) {
@@ -392,8 +420,8 @@ static u32 do_xdp_prog(struct virtnet_info *vi,
 		qp = vi->curr_queue_pairs -
 			vi->xdp_queue_pairs +
 			smp_processor_id();
-		xdp.data = buf + (vi->mergeable_rx_bufs ? 0 : 4);
-		virtnet_xdp_xmit(vi, rq, &vi->sq[qp], &xdp);
+		xdp.data = buf;
+		virtnet_xdp_xmit(vi, rq, &vi->sq[qp], &xdp, data);
 		return XDP_TX;
 	default:
 		bpf_warn_invalid_xdp_action(act);
@@ -403,14 +431,47 @@ static u32 do_xdp_prog(struct virtnet_info *vi,
 	}
 }
 
-static struct sk_buff *receive_small(struct virtnet_info *vi, void *buf,
unsigned int len)
+static struct sk_buff *receive_small(struct net_device *dev,
+				     struct virtnet_info *vi,
+				     struct receive_queue *rq,
+				     void *buf, unsigned int len)
 {
 	struct sk_buff * skb = buf;
+	struct bpf_prog *xdp_prog;
 
 	len -= vi->hdr_len;
 	skb_trim(skb, len);
 
+	rcu_read_lock();
+	xdp_prog = rcu_dereference(rq->xdp_prog);
+	if (xdp_prog) {
+		struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
+		u32 act;
+
+		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
+			goto err_xdp;
+		act = do_xdp_prog(vi, rq, xdp_prog, skb, len);
+		switch (act) {
+		case XDP_PASS:
+			break;
+		case XDP_TX:
+			rcu_read_unlock();
+			goto xdp_xmit;
+		case XDP_DROP:
+		default:
+			goto err_xdp;
+		}
+	}
+	rcu_read_unlock();
+
 	return skb;
+
+err_xdp:
+	rcu_read_unlock();
+	dev->stats.rx_dropped++;
+	kfree_skb(skb);
+xdp_xmit:
+	return NULL;
 }
 
 static struct sk_buff *receive_big(struct net_device *dev,
@@ -537,7 +598,8 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 		if (unlikely(hdr->hdr.gso_type))
 			goto err_xdp;
 
-		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
+		act = do_xdp_prog(vi, rq, xdp_prog,
+				  page_address(xdp_page) + offset, len);
 		switch (act) {
 		case XDP_PASS:
 			/* We can only create skb based on xdp_page. */
@@ -672,7 +734,7 @@ static void receive_buf(struct virtnet_info *vi, struct
receive_queue *rq,
 	else if (vi->big_packets)
 		skb = receive_big(dev, vi, rq, buf, len);
 	else
-		skb = receive_small(vi, buf, len);
+		skb = receive_small(dev, vi, rq, buf, len);
 
 	if (unlikely(!skb))
 		return;
-- 
2.7.4

On 16-12-23 06:37 AM, Jason Wang wrote:
> After we linearize page, we should xmit this page instead of the page
> of first buffer which may lead unexpected result. With this patch, we
> can see correct packet during XDP_TX.
> 
> Cc: John Fastabend <john.r.fastabend at intel.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/net/virtio_net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 1067253..fe4562d 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -572,7 +572,7 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>  		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
>  			goto err_xdp;
>  
> -		act = do_xdp_prog(vi, rq, xdp_prog, page, offset, len);
> +		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
>  		switch (act) {
>  		case XDP_PASS:
>  			if (unlikely(xdp_page != page))
> 
Thanks clumsy merge conflict resolution between v4 and v6 versions :/

Acked-by: John Fastabend <john.r.fastabend at intel.com>

On 16-12-23 06:37 AM, Jason Wang wrote:
> We don't put page during linearizing, the would cause leaking when
> xmit through XDP_TX or the packet exceeds PAGE_SIZE. Fix them by
> put page accordingly. Also decrease the number of buffers during
> linearizing to make sure caller can free buffers correctly when packet
> exceeds PAGE_SIZE. With this patch, we won't get OOM after linearize
> huge number of packets.
> 
> Cc: John Fastabend <john.r.fastabend at intel.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
Thanks! looks good. By the way do you happen to have any actual
configuration where this path is hit? I obviously didn't test this
very long other than a quick test with my hacked vhost driver.

Acked-by: John Fastabend <john.r.fastabend at intel.com>

On 16-12-23 06:37 AM, Jason Wang wrote:
> When XDP_PASS were determined for linearized packets, we try to get
> new buffers in the virtqueue and build skbs from them. This is wrong,
> we should create skbs based on existed buffers instead. Fixing them by
> creating skb based on xdp_page.
> 
> With this patch "ping 192.168.100.4 -s 3900 -M do" works for
XDP_PASS.
> 
> Cc: John Fastabend <john.r.fastabend at intel.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/net/virtio_net.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 58ad40e..470293e 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -578,8 +578,14 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>  		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
>  		switch (act) {
>  		case XDP_PASS:
> -			if (unlikely(xdp_page != page))
> -				__free_pages(xdp_page, 0);
> +			/* We can only create skb based on xdp_page. */
> +			if (unlikely(xdp_page != page)) {
> +				rcu_read_unlock();
> +				put_page(page);
> +				head_skb = page_to_skb(vi, rq, xdp_page,
> +						       0, len, PAGE_SIZE);
> +				return head_skb;
> +			}
>  			break;
>  		case XDP_TX:
>  			if (unlikely(xdp_page != page))
> 
Great thanks. This was likely working before because of the memory
leak fixed in 3/9.

Acked-by: John Fastabend <john.r.fastabend at intel.com>

On 16-12-23 06:37 AM, Jason Wang wrote:
> We drop csumed packet when do XDP for packets. This breaks
> XDP_PASS when GUEST_CSUM is supported. Fix this by allowing csum flag
> to be set. With this patch, simple TCP works for XDP_PASS.
> 
> Cc: John Fastabend <john.r.fastabend at intel.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/net/virtio_net.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 470293e..0778dc8 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -440,7 +440,7 @@ static struct sk_buff *receive_big(struct net_device
*dev,
>  		struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
>  		u32 act;
>  
> -		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
> +		if (unlikely(hdr->hdr.gso_type))
>  			goto err_xdp;
>  		act = do_xdp_prog(vi, rq, xdp_prog, page, 0, len);
>  		switch (act) {
> @@ -572,7 +572,7 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>  		 * the receive path after XDP is loaded. In practice I
>  		 * was not able to create this condition.
>  		 */
> -		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
> +		if (unlikely(hdr->hdr.gso_type))
>  			goto err_xdp;
>  
>  		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
> 
Acked-by: John Fastabend <john.r.fastabend at intel.com>

On 16-12-23 06:37 AM, Jason Wang wrote:
> We don't update ewma rx buf size in the case of XDP. This will lead
> underestimation of rx buf size which causes host to produce more than
> one buffers. This will greatly increase the possibility of XDP page
> linearization.
> 
> Cc: John Fastabend <john.r.fastabend at intel.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/net/virtio_net.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0778dc8..77ae358 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -584,10 +584,12 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>  				put_page(page);
>  				head_skb = page_to_skb(vi, rq, xdp_page,
>  						       0, len, PAGE_SIZE);
> +				ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
>  				return head_skb;
>  			}
>  			break;
>  		case XDP_TX:
> +			ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
>  			if (unlikely(xdp_page != page))
>  				goto err_xdp;
>  			rcu_read_unlock();
> @@ -596,6 +598,7 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>  		default:
>  			if (unlikely(xdp_page != page))
>  				__free_pages(xdp_page, 0);
> +			ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
>  			goto err_xdp;
>  		}
>  	}
> 
Looks needed although I guess it will only be the case with
MTU > ETH_DATA_LEN because of the clamp in get_mergeable_buf_len().
Although XDP setup allows MTU up to page_size - hdr so certainly
will happen with ~MTU > 1500.

I need to add some various MTU tests to my setup.

Acked-by: John Fastabend <john.r.fastabend at intel.com>

On 16-12-23 06:37 AM, Jason Wang wrote:
> When VIRTIO_NET_F_GUEST_UFO is negotiated, host could still send UFO
> packet that exceeds a single page which could not be handled
> correctly by XDP. So this patch forbids setting XDP when GUEST_UFO is
> supported. While at it, forbid XDP for ECN (which comes only from GRO)
> too to prevent user from misconfiguration.
> 
> Cc: John Fastabend <john.r.fastabend at intel.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/net/virtio_net.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 77ae358..c1f66d8 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1684,7 +1684,9 @@ static int virtnet_xdp_set(struct net_device *dev,
struct bpf_prog *prog)
>  	int i, err;
>  
>  	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> -	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6)) {
> +	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
> +	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
> +	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO)) {
>  		netdev_warn(dev, "can't set XDP while host is implementing LRO,
disable LRO first\n");
>  		return -EOPNOTSUPP;
>  	}
> 
Acked-by: John Fastabend <john.r.fastabend at intel.com>

On 16-12-23 06:37 AM, Jason Wang wrote:
> Commit f600b6905015 ("virtio_net: Add XDP support") leaves the
case of
> small receive buffer untouched. This will confuse the user who want to
> set XDP but use small buffers. Other than forbid XDP in small buffer
> mode, let's make it work. XDP then can only work at skb->data since
> virtio-net create skbs during refill, this is sub optimal which could
> be optimized in the future.
> 
> Cc: John Fastabend <john.r.fastabend at intel.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---

Looks good to me thanks!

Acked-by: John Fastabend <john.r.fastabend at intel.com>

On 16-12-23 06:37 AM, Jason Wang wrote:
> Merry Xmas and a Happy New year to all:
> 
> This series tries to fixes several issues for virtio-net XDP which
> could be categorized into several parts:
> 
> - fix several issues during XDP linearizing
> - allow csumed packet to work for XDP_PASS
> - make EWMA rxbuf size estimation works for XDP
> - forbid XDP when GUEST_UFO is support
> - remove big packet XDP support
> - add XDP support or small buffer
> 
> Please see individual patches for details.
> 
> Thanks
> 
> Jason Wang (9):
>   virtio-net: remove the warning before XDP linearizing
>   virtio-net: correctly xmit linearized page on XDP_TX
>   virtio-net: fix page miscount during XDP linearizing
>   virtio-net: correctly handle XDP_PASS for linearized packets
>   virtio-net: unbreak csumed packets for XDP_PASS
>   virtio-net: make rx buf size estimation works for XDP
>   virtio-net: forbid XDP when VIRTIO_NET_F_GUEST_UFO is support
>   virtio-net: remove big packet XDP codes
>   virtio-net: XDP support for small buffers
> 
>  drivers/net/virtio_net.c | 172
++++++++++++++++++++++++++++-------------------
>  1 file changed, 102 insertions(+), 70 deletions(-)
> 
Thanks a lot Jason. The last piece that is needed is support to
complete XDP support is to get the adjust_head part correct. I'll
send out a patch in a bit but will need to merge it on top of this
set.

.John

From: Jason Wang <jasowang at redhat.com>
Date: Fri, 23 Dec 2016 22:37:23 +0800
> Merry Xmas and a Happy New year to all:
> 
> This series tries to fixes several issues for virtio-net XDP which
> could be categorized into several parts:
> 
> - fix several issues during XDP linearizing
> - allow csumed packet to work for XDP_PASS
> - make EWMA rxbuf size estimation works for XDP
> - forbid XDP when GUEST_UFO is support
> - remove big packet XDP support
> - add XDP support or small buffer
> 
> Please see individual patches for details.
Series applied, thanks Jason.

Hi Jason,

On 12/23/2016 03:37 PM, Jason Wang wrote:
> Since we use EWMA to estimate the size of rx buffer. When rx buffer
> size is underestimated, it's usual to have a packet with more than one
> buffers. Consider this is not a bug, remove the warning and correct
> the comment before XDP linearizing.
>
> Cc: John Fastabend <john.r.fastabend at intel.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>   drivers/net/virtio_net.c | 8 +-------
>   1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 08327e0..1067253 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -552,14 +552,8 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>   		struct page *xdp_page;
>   		u32 act;
>
> -		/* No known backend devices should send packets with
> -		 * more than a single buffer when XDP conditions are
> -		 * met. However it is not strictly illegal so the case
> -		 * is handled as an exception and a warning is thrown.
> -		 */
> +		/* This happens when rx buffer size is underestimated */
>   		if (unlikely(num_buf > 1)) {
> -			bpf_warn_invalid_xdp_buffer();
Could you also remove the bpf_warn_invalid_xdp_buffer(), which got added
just for this?

Thanks.
>   			/* linearize data for XDP */
>   			xdp_page = xdp_linearize_page(rq, num_buf,
>   						      page, offset, &len);
>

On 2016?12?24? 01:10, John Fastabend wrote:
> On 16-12-23 06:37 AM, Jason Wang wrote:
>> Merry Xmas and a Happy New year to all:
>>
>> This series tries to fixes several issues for virtio-net XDP which
>> could be categorized into several parts:
>>
>> - fix several issues during XDP linearizing
>> - allow csumed packet to work for XDP_PASS
>> - make EWMA rxbuf size estimation works for XDP
>> - forbid XDP when GUEST_UFO is support
>> - remove big packet XDP support
>> - add XDP support or small buffer
>>
>> Please see individual patches for details.
>>
>> Thanks
>>
>> Jason Wang (9):
>>    virtio-net: remove the warning before XDP linearizing
>>    virtio-net: correctly xmit linearized page on XDP_TX
>>    virtio-net: fix page miscount during XDP linearizing
>>    virtio-net: correctly handle XDP_PASS for linearized packets
>>    virtio-net: unbreak csumed packets for XDP_PASS
>>    virtio-net: make rx buf size estimation works for XDP
>>    virtio-net: forbid XDP when VIRTIO_NET_F_GUEST_UFO is support
>>    virtio-net: remove big packet XDP codes
>>    virtio-net: XDP support for small buffers
>>
>>   drivers/net/virtio_net.c | 172
++++++++++++++++++++++++++++-------------------
>>   1 file changed, 102 insertions(+), 70 deletions(-)
>>
> Thanks a lot Jason. The last piece that is needed is support to
> complete XDP support is to get the adjust_head part correct. I'll
> send out a patch in a bit but will need to merge it on top of this
> set.
>
> .John
Yes, glad to see the your patch.

Thanks.

On 16-12-23 06:37 AM, Jason Wang wrote:
> Commit f600b6905015 ("virtio_net: Add XDP support") leaves the
case of
> small receive buffer untouched. This will confuse the user who want to
> set XDP but use small buffers. Other than forbid XDP in small buffer
> mode, let's make it work. XDP then can only work at skb->data since
> virtio-net create skbs during refill, this is sub optimal which could
> be optimized in the future.
> 
> Cc: John Fastabend <john.r.fastabend at intel.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/net/virtio_net.c | 112
++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 87 insertions(+), 25 deletions(-)
> 
Hi Jason,

I was doing some more testing on this what do you think about doing this
so that free_unused_bufs() handles the buffer free with dev_kfree_skb()
instead of put_page in small receive mode. Seems more correct to me.


diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 783e842..27ff76c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1898,6 +1898,10 @@ static void free_receive_page_frags(struct virtnet_info
*vi)

 static bool is_xdp_queue(struct virtnet_info *vi, int q)
 {
+       /* For small receive mode always use kfree_skb variants */
+       if (!vi->mergeable_rx_bufs)
+               return false;
+
        if (q < (vi->curr_queue_pairs - vi->xdp_queue_pairs))
                return false;
        else if (q < vi->curr_queue_pairs)


patch is untested just spotted doing code review.

Thanks,
John