[net PATCH 0/5] virtio_net XDP fixes and ajust_header xupport

[net PATCH 0/5] virtio_net XDP fixes and ajust_header xupport

[John Fastabend]

This has a fix to handle small buffer free logic correctly and then
also adds adjust head support.

I pushed adjust head at net (even though its rc3) to avoid having
to push another exception case into virtio_net to catch if the
program uses adjust_head and then block it. If there are any strong
objections to this we can push it at net-next and use a patch from
Jakub to add the exception handling but then user space has to deal
with it either via try/fail logic or via kernel version checks. Granted
we already have some cases that need to be configured to enable XDP
but I don't see any reason to have yet another one when we can fix it
now vs delaying a kernel version.

---

John Fastabend (5):
      virtio_net: use dev_kfree_skb for small buffer XDP receive
      net: virtio: wrap rtnl_lock in test for calling with lock already held
      virtio_net: factor out xdp handler for readability
      virtio_net: remove duplicate queue pair binding in XDP
      virtio_net: XDP support for adjust_head


 drivers/net/virtio_net.c |  251 ++++++++++++++++++++++++++++++++--------------
 drivers/virtio/virtio.c  |    9 +-
 include/linux/virtio.h   |    3 +
 3 files changed, 183 insertions(+), 80 deletions(-)

[net PATCH 1/5] virtio_net: use dev_kfree_skb for small buffer XDP receive

[John Fastabend]

In the small buffer case during driver unload we currently use
put_page instead of dev_kfree_skb. Resolve this by adding a check
for virtnet mode when checking XDP queue type. Also name the
function so that the code reads correctly to match the additional
check.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
---
 drivers/net/virtio_net.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4a10500..d97bb71 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1890,8 +1890,12 @@ static void free_receive_page_frags(struct virtnet_info *vi)
 			put_page(vi->rq[i].alloc_frag.page);
 }
 
-static bool is_xdp_queue(struct virtnet_info *vi, int q)
+static bool is_xdp_raw_buffer_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)
@@ -1908,7 +1912,7 @@ static void free_unused_bufs(struct virtnet_info *vi)
 	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_queue(vi, i))
+			if (!is_xdp_raw_buffer_queue(vi, i))
 				dev_kfree_skb(buf);
 			else
 				put_page(virt_to_head_page(buf));

[net PATCH 2/5] net: virtio: wrap rtnl_lock in test for calling with lock already held

[John Fastabend]

For XDP use case and to allow ethtool reset tests it is useful to be
able to use reset routines from contexts where rtnl lock is already
held.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
---
 drivers/net/virtio_net.c |   16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index d97bb71..43cb2e0 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1864,12 +1864,13 @@ static void virtnet_free_queues(struct virtnet_info *vi)
 	kfree(vi->sq);
 }
 
-static void free_receive_bufs(struct virtnet_info *vi)
+static void free_receive_bufs(struct virtnet_info *vi, bool need_lock)
 {
 	struct bpf_prog *old_prog;
 	int i;
 
-	rtnl_lock();
+	if (need_lock)
+		rtnl_lock();
 	for (i = 0; i < vi->max_queue_pairs; i++) {
 		while (vi->rq[i].pages)
 			__free_pages(get_a_page(&vi->rq[i], GFP_KERNEL), 0);
@@ -1879,7 +1880,8 @@ static void free_receive_bufs(struct virtnet_info *vi)
 		if (old_prog)
 			bpf_prog_put(old_prog);
 	}
-	rtnl_unlock();
+	if (need_lock)
+		rtnl_unlock();
 }
 
 static void free_receive_page_frags(struct virtnet_info *vi)
@@ -2351,14 +2353,14 @@ static int virtnet_probe(struct virtio_device *vdev)
 	return err;
 }
 
-static void remove_vq_common(struct virtnet_info *vi)
+static void remove_vq_common(struct virtnet_info *vi, bool lock)
 {
 	vi->vdev->config->reset(vi->vdev);
 
 	/* Free unused buffers in both send and recv, if any. */
 	free_unused_bufs(vi);
 
-	free_receive_bufs(vi);
+	free_receive_bufs(vi, lock);
 
 	free_receive_page_frags(vi);
 
@@ -2376,7 +2378,7 @@ static void virtnet_remove(struct virtio_device *vdev)
 
 	unregister_netdev(vi->dev);
 
-	remove_vq_common(vi);
+	remove_vq_common(vi, true);
 
 	free_percpu(vi->stats);
 	free_netdev(vi->dev);
@@ -2401,7 +2403,7 @@ static int virtnet_freeze(struct virtio_device *vdev)
 			napi_disable(&vi->rq[i].napi);
 	}
 
-	remove_vq_common(vi);
+	remove_vq_common(vi, true);
 
 	return 0;
 }

[net PATCH 3/5] virtio_net: factor out xdp handler for readability

[John Fastabend]

At this point the do_xdp_prog is mostly if/else branches handling
the different modes of virtio_net. So remove it and handle running
the program in the per mode handlers.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
---
 drivers/net/virtio_net.c |   76 +++++++++++++++++-----------------------------
 1 file changed, 28 insertions(+), 48 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 43cb2e0..ec54644 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -388,49 +388,6 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
 	virtqueue_kick(sq->vq);
 }
 
-static u32 do_xdp_prog(struct virtnet_info *vi,
-		       struct receive_queue *rq,
-		       struct bpf_prog *xdp_prog,
-		       void *data, int len)
-{
-	int hdr_padded_len;
-	struct xdp_buff xdp;
-	void *buf;
-	unsigned int qp;
-	u32 act;
-
-	if (vi->mergeable_rx_bufs) {
-		hdr_padded_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
-		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 = skb->data;
-		xdp.data_end = xdp.data + len;
-		buf = skb->data;
-	}
-
-	act = bpf_prog_run_xdp(xdp_prog, &xdp);
-	switch (act) {
-	case XDP_PASS:
-		return XDP_PASS;
-	case XDP_TX:
-		qp = vi->curr_queue_pairs -
-			vi->xdp_queue_pairs +
-			smp_processor_id();
-		xdp.data = buf;
-		virtnet_xdp_xmit(vi, rq, &vi->sq[qp], &xdp, data);
-		return XDP_TX;
-	default:
-		bpf_warn_invalid_xdp_action(act);
-	case XDP_ABORTED:
-	case XDP_DROP:
-		return XDP_DROP;
-	}
-}
-
 static struct sk_buff *receive_small(struct net_device *dev,
 				     struct virtnet_info *vi,
 				     struct receive_queue *rq,
@@ -446,19 +403,30 @@ static struct sk_buff *receive_small(struct net_device *dev,
 	xdp_prog = rcu_dereference(rq->xdp_prog);
 	if (xdp_prog) {
 		struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
+		struct xdp_buff xdp;
+		unsigned int qp;
 		u32 act;
 
 		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
 			goto err_xdp;
-		act = do_xdp_prog(vi, rq, xdp_prog, skb, len);
+
+		xdp.data = skb->data;
+		xdp.data_end = xdp.data + len;
+		act = bpf_prog_run_xdp(xdp_prog, &xdp);
 		switch (act) {
 		case XDP_PASS:
 			break;
 		case XDP_TX:
+			qp = vi->curr_queue_pairs -
+				vi->xdp_queue_pairs +
+				smp_processor_id();
+			virtnet_xdp_xmit(vi, rq, &vi->sq[qp], &xdp, skb);
 			rcu_read_unlock();
 			goto xdp_xmit;
-		case XDP_DROP:
 		default:
+			bpf_warn_invalid_xdp_action(act);
+		case XDP_ABORTED:
+		case XDP_DROP:
 			goto err_xdp;
 		}
 	}
@@ -575,7 +543,11 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 	rcu_read_lock();
 	xdp_prog = rcu_dereference(rq->xdp_prog);
 	if (xdp_prog) {
+		int desc_room = sizeof(struct virtio_net_hdr_mrg_rxbuf);
 		struct page *xdp_page;
+		struct xdp_buff xdp;
+		unsigned int qp;
+		void *data;
 		u32 act;
 
 		/* This happens when rx buffer size is underestimated */
@@ -598,8 +570,10 @@ 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,
-				  page_address(xdp_page) + offset, len);
+		data = page_address(xdp_page) + offset;
+		xdp.data = data + desc_room;
+		xdp.data_end = xdp.data + (len - vi->hdr_len);
+		act = bpf_prog_run_xdp(xdp_prog, &xdp);
 		switch (act) {
 		case XDP_PASS:
 			/* We can only create skb based on xdp_page. */
@@ -613,13 +587,19 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 			}
 			break;
 		case XDP_TX:
+			qp = vi->curr_queue_pairs -
+				vi->xdp_queue_pairs +
+				smp_processor_id();
+			virtnet_xdp_xmit(vi, rq, &vi->sq[qp], &xdp, data);
 			ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
 			if (unlikely(xdp_page != page))
 				goto err_xdp;
 			rcu_read_unlock();
 			goto xdp_xmit;
-		case XDP_DROP:
 		default:
+			bpf_warn_invalid_xdp_action(act);
+		case XDP_ABORTED:
+		case XDP_DROP:
 			if (unlikely(xdp_page != page))
 				__free_pages(xdp_page, 0);
 			ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);

[net PATCH 4/5] virtio_net: remove duplicate queue pair binding in XDP

[John Fastabend]

Factor out qp assignment.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
---
 drivers/net/virtio_net.c |   18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ec54644..6041828 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -332,15 +332,19 @@ 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,
 			     void *data)
 {
 	struct virtio_net_hdr_mrg_rxbuf *hdr;
 	unsigned int num_sg, len;
+	struct send_queue *sq;
+	unsigned int qp;
 	void *xdp_sent;
 	int err;
 
+	qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
+	sq = &vi->sq[qp];
+
 	/* Free up any pending old buffers before queueing new ones. */
 	while ((xdp_sent = virtqueue_get_buf(sq->vq, &len)) != NULL) {
 		if (vi->mergeable_rx_bufs) {
@@ -404,7 +408,6 @@ static struct sk_buff *receive_small(struct net_device *dev,
 	if (xdp_prog) {
 		struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
 		struct xdp_buff xdp;
-		unsigned int qp;
 		u32 act;
 
 		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
@@ -417,10 +420,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
 		case XDP_PASS:
 			break;
 		case XDP_TX:
-			qp = vi->curr_queue_pairs -
-				vi->xdp_queue_pairs +
-				smp_processor_id();
-			virtnet_xdp_xmit(vi, rq, &vi->sq[qp], &xdp, skb);
+			virtnet_xdp_xmit(vi, rq, &xdp, skb);
 			rcu_read_unlock();
 			goto xdp_xmit;
 		default:
@@ -546,7 +546,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 		int desc_room = sizeof(struct virtio_net_hdr_mrg_rxbuf);
 		struct page *xdp_page;
 		struct xdp_buff xdp;
-		unsigned int qp;
 		void *data;
 		u32 act;
 
@@ -587,10 +586,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 			}
 			break;
 		case XDP_TX:
-			qp = vi->curr_queue_pairs -
-				vi->xdp_queue_pairs +
-				smp_processor_id();
-			virtnet_xdp_xmit(vi, rq, &vi->sq[qp], &xdp, data);
+			virtnet_xdp_xmit(vi, rq, &xdp, data);
 			ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
 			if (unlikely(xdp_page != page))
 				goto err_xdp;

[net PATCH 5/5] virtio_net: XDP support for adjust_head

[John Fastabend]

Add support for XDP adjust head by allocating a 256B header region
that XDP programs can grow into. This is only enabled when a XDP
program is loaded.

In order to ensure that we do not have to unwind queue headroom push
queue setup below bpf_prog_add. It reads better to do a prog ref
unwind vs another queue setup call.

At the moment this code must do a full reset to ensure old buffers
without headroom on program add or with headroom on program removal
are not used incorrectly in the datapath. Ideally we would only
have to disable/enable the RX queues being updated but there is no
API to do this at the moment in virtio so use the big hammer. In
practice it is likely not that big of a problem as this will only
happen when XDP is enabled/disabled changing programs does not
require the reset. There is some risk that the driver may either
have an allocation failure or for some reason fail to correctly
negotiate with the underlying backend in this case the driver will
be left uninitialized. I have not seen this ever happen on my test
systems and for what its worth this same failure case can occur
from probe and other contexts in virtio framework.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
---
 drivers/net/virtio_net.c |  155 ++++++++++++++++++++++++++++++++++++++++------
 drivers/virtio/virtio.c  |    9 ++-
 include/linux/virtio.h   |    3 +
 3 files changed, 144 insertions(+), 23 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 6041828..8b897e7 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -28,6 +28,7 @@
 #include <linux/slab.h>
 #include <linux/cpu.h>
 #include <linux/average.h>
+#include <linux/pci.h>
 #include <net/busy_poll.h>
 
 static int napi_weight = NAPI_POLL_WEIGHT;
@@ -159,6 +160,9 @@ struct virtnet_info {
 	/* Ethtool settings */
 	u8 duplex;
 	u32 speed;
+
+	/* Headroom allocated in RX Queue */
+	unsigned int headroom;
 };
 
 struct padded_vnet_hdr {
@@ -359,6 +363,7 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
 	}
 
 	if (vi->mergeable_rx_bufs) {
+		xdp->data -= sizeof(struct virtio_net_hdr_mrg_rxbuf);
 		/* Zero header and leave csum up to XDP layers */
 		hdr = xdp->data;
 		memset(hdr, 0, vi->hdr_len);
@@ -375,7 +380,9 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
 		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);
+		skb_to_sgvec(skb, sq->sg + 1,
+			     xdp->data - xdp->data_hard_start,
+			     xdp->data_end - xdp->data);
 	}
 	err = virtqueue_add_outbuf(sq->vq, sq->sg, num_sg,
 				   data, GFP_ATOMIC);
@@ -401,7 +408,6 @@ static struct sk_buff *receive_small(struct net_device *dev,
 	struct bpf_prog *xdp_prog;
 
 	len -= vi->hdr_len;
-	skb_trim(skb, len);
 
 	rcu_read_lock();
 	xdp_prog = rcu_dereference(rq->xdp_prog);
@@ -413,11 +419,15 @@ static struct sk_buff *receive_small(struct net_device *dev,
 		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
 			goto err_xdp;
 
-		xdp.data = skb->data;
+		xdp.data_hard_start = skb->data;
+		xdp.data = skb->data + vi->headroom;
 		xdp.data_end = xdp.data + len;
 		act = bpf_prog_run_xdp(xdp_prog, &xdp);
 		switch (act) {
 		case XDP_PASS:
+			/* Recalculate length in case bpf program changed it */
+			len = xdp.data_end - xdp.data;
+			__skb_pull(skb, xdp.data - xdp.data_hard_start);
 			break;
 		case XDP_TX:
 			virtnet_xdp_xmit(vi, rq, &xdp, skb);
@@ -432,6 +442,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
 	}
 	rcu_read_unlock();
 
+	skb_trim(skb, len);
 	return skb;
 
 err_xdp:
@@ -569,7 +580,11 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 		if (unlikely(hdr->hdr.gso_type))
 			goto err_xdp;
 
+		/* Allow consuming headroom but reserve enough space to push
+		 * the descriptor on if we get an XDP_TX return code.
+		 */
 		data = page_address(xdp_page) + offset;
+		xdp.data_hard_start = data - vi->headroom + desc_room;
 		xdp.data = data + desc_room;
 		xdp.data_end = xdp.data + (len - vi->hdr_len);
 		act = bpf_prog_run_xdp(xdp_prog, &xdp);
@@ -748,20 +763,21 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
 static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
 			     gfp_t gfp)
 {
+	int headroom = GOOD_PACKET_LEN + vi->headroom;
 	struct sk_buff *skb;
 	struct virtio_net_hdr_mrg_rxbuf *hdr;
 	int err;
 
-	skb = __netdev_alloc_skb_ip_align(vi->dev, GOOD_PACKET_LEN, gfp);
+	skb = __netdev_alloc_skb_ip_align(vi->dev, headroom, gfp);
 	if (unlikely(!skb))
 		return -ENOMEM;
 
-	skb_put(skb, GOOD_PACKET_LEN);
+	skb_put(skb, headroom);
 
 	hdr = skb_vnet_hdr(skb);
 	sg_init_table(rq->sg, 2);
 	sg_set_buf(rq->sg, hdr, vi->hdr_len);
-	skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);
+	skb_to_sgvec(skb, rq->sg + 1, vi->headroom, skb->len - vi->headroom);
 
 	err = virtqueue_add_inbuf(rq->vq, rq->sg, 2, skb, gfp);
 	if (err < 0)
@@ -829,24 +845,27 @@ static unsigned int get_mergeable_buf_len(struct ewma_pkt_len *avg_pkt_len)
 	return ALIGN(len, MERGEABLE_BUFFER_ALIGN);
 }
 
-static int add_recvbuf_mergeable(struct receive_queue *rq, gfp_t gfp)
+static int add_recvbuf_mergeable(struct virtnet_info *vi,
+				 struct receive_queue *rq, gfp_t gfp)
 {
 	struct page_frag *alloc_frag = &rq->alloc_frag;
+	unsigned int headroom = vi->headroom;
 	char *buf;
 	unsigned long ctx;
 	int err;
 	unsigned int len, hole;
 
 	len = get_mergeable_buf_len(&rq->mrg_avg_pkt_len);
-	if (unlikely(!skb_page_frag_refill(len, alloc_frag, gfp)))
+	if (unlikely(!skb_page_frag_refill(len + headroom, alloc_frag, gfp)))
 		return -ENOMEM;
 
 	buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
+	buf += headroom; /* advance address leaving hole at front of pkt */
 	ctx = mergeable_buf_to_ctx(buf, len);
 	get_page(alloc_frag->page);
-	alloc_frag->offset += len;
+	alloc_frag->offset += len + headroom;
 	hole = alloc_frag->size - alloc_frag->offset;
-	if (hole < len) {
+	if (hole < len + headroom) {
 		/* To avoid internal fragmentation, if there is very likely not
 		 * enough space for another buffer, add the remaining space to
 		 * the current buffer. This extra space is not included in
@@ -880,7 +899,7 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
 	gfp |= __GFP_COLD;
 	do {
 		if (vi->mergeable_rx_bufs)
-			err = add_recvbuf_mergeable(rq, gfp);
+			err = add_recvbuf_mergeable(vi, rq, gfp);
 		else if (vi->big_packets)
 			err = add_recvbuf_big(vi, rq, gfp);
 		else
@@ -1675,12 +1694,90 @@ static void virtnet_init_settings(struct net_device *dev)
 	.set_settings = virtnet_set_settings,
 };
 
+#define VIRTIO_XDP_HEADROOM 256
+
+static int init_vqs(struct virtnet_info *vi);
+static void remove_vq_common(struct virtnet_info *vi, bool lock);
+
+/* Reset virtio device with RTNL held this is very similar to the
+ * freeze()/restore() logic except we need to ensure locking. It is
+ * possible that this routine may fail and leave the driver in a
+ * failed state. However assuming the driver negotiated correctly
+ * at probe time we _should_ be able to (re)negotiate driver again.
+ */
+static int virtnet_xdp_reset(struct virtnet_info *vi)
+{
+	struct virtio_device *vdev = vi->vdev;
+	unsigned int status;
+	int i, ret;
+
+	/* Disable and unwind rings */
+	virtio_config_disable(vdev);
+	vdev->failed = vdev->config->get_status(vdev) & VIRTIO_CONFIG_S_FAILED;
+
+	netif_device_detach(vi->dev);
+	cancel_delayed_work_sync(&vi->refill);
+	if (netif_running(vi->dev)) {
+		for (i = 0; i < vi->max_queue_pairs; i++)
+			napi_disable(&vi->rq[i].napi);
+	}
+
+	remove_vq_common(vi, false);
+
+	/* Do a reset per virtio spec recommendation */
+	vdev->config->reset(vdev);
+
+	/* Acknowledge that we've seen the device. */
+	status = vdev->config->get_status(vdev);
+	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_ACKNOWLEDGE);
+
+	/* Notify driver is up and finalize features per specification. The
+	 * error code from finalize features is checked here but should not
+	 * fail because we assume features were previously synced successfully.
+	 */
+	status = vdev->config->get_status(vdev);
+	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_DRIVER);
+	ret = virtio_finalize_features(vdev);
+	if (ret) {
+		netdev_warn(vi->dev, "virtio_finalize_features failed during reset aborting\n");
+		goto err;
+	}
+
+	ret = init_vqs(vi);
+	if (ret) {
+		netdev_warn(vi->dev, "init_vqs failed during reset aborting\n");
+		goto err;
+	}
+	virtio_device_ready(vi->vdev);
+
+	if (netif_running(vi->dev)) {
+		for (i = 0; i < vi->curr_queue_pairs; i++)
+			if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
+				schedule_delayed_work(&vi->refill, 0);
+
+		for (i = 0; i < vi->max_queue_pairs; i++)
+			virtnet_napi_enable(&vi->rq[i]);
+	}
+	netif_device_attach(vi->dev);
+	/* Finally, tell the device we're all set */
+	status = vdev->config->get_status(vdev);
+	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_DRIVER_OK);
+	virtio_config_enable(vdev);
+
+	return 0;
+err:
+	status = vdev->config->get_status(vdev);
+	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_FAILED);
+	return ret;
+}
+
 static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
 {
 	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
 	struct virtnet_info *vi = netdev_priv(dev);
 	struct bpf_prog *old_prog;
 	u16 xdp_qp = 0, curr_qp;
+	unsigned int old_hr;
 	int i, err;
 
 	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
@@ -1712,18 +1809,31 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
 		return -ENOMEM;
 	}
 
-	err = virtnet_set_queues(vi, curr_qp + xdp_qp);
-	if (err) {
-		dev_warn(&dev->dev, "XDP Device queue allocation failure.\n");
-		return err;
-	}
-
+	old_hr = vi->headroom;
 	if (prog) {
 		prog = bpf_prog_add(prog, vi->max_queue_pairs - 1);
-		if (IS_ERR(prog)) {
-			virtnet_set_queues(vi, curr_qp);
+		if (IS_ERR(prog))
 			return PTR_ERR(prog);
-		}
+		vi->headroom = VIRTIO_XDP_HEADROOM;
+	} else {
+		vi->headroom = 0;
+	}
+
+	/* Changing the headroom in buffers is a disruptive operation because
+	 * existing buffers must be flushed and reallocated. This will happen
+	 * when a xdp program is initially added or xdp is disabled by removing
+	 * the xdp program.
+	 */
+	if (old_hr != vi->headroom) {
+		err = virtnet_xdp_reset(vi);
+		if (err)
+			goto err_reset;
+	}
+
+	err = virtnet_set_queues(vi, curr_qp + xdp_qp);
+	if (err) {
+		dev_warn(&dev->dev, "XDP Device queue allocation failure.\n");
+		goto err_reset;
 	}
 
 	vi->xdp_queue_pairs = xdp_qp;
@@ -1737,6 +1847,11 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
 	}
 
 	return 0;
+err_reset:
+	if (prog)
+		bpf_prog_sub(prog, vi->max_queue_pairs - 1);
+	vi->headroom = old_hr;
+	return err;
 }
 
 static bool virtnet_xdp_query(struct net_device *dev)
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 7062bb0..0e922b9 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -145,14 +145,15 @@ void virtio_config_changed(struct virtio_device *dev)
 }
 EXPORT_SYMBOL_GPL(virtio_config_changed);
 
-static void virtio_config_disable(struct virtio_device *dev)
+void virtio_config_disable(struct virtio_device *dev)
 {
 	spin_lock_irq(&dev->config_lock);
 	dev->config_enabled = false;
 	spin_unlock_irq(&dev->config_lock);
 }
+EXPORT_SYMBOL_GPL(virtio_config_disable);
 
-static void virtio_config_enable(struct virtio_device *dev)
+void virtio_config_enable(struct virtio_device *dev)
 {
 	spin_lock_irq(&dev->config_lock);
 	dev->config_enabled = true;
@@ -161,8 +162,9 @@ static void virtio_config_enable(struct virtio_device *dev)
 	dev->config_change_pending = false;
 	spin_unlock_irq(&dev->config_lock);
 }
+EXPORT_SYMBOL_GPL(virtio_config_enable);
 
-static int virtio_finalize_features(struct virtio_device *dev)
+int virtio_finalize_features(struct virtio_device *dev)
 {
 	int ret = dev->config->finalize_features(dev);
 	unsigned status;
@@ -182,6 +184,7 @@ static int virtio_finalize_features(struct virtio_device *dev)
 	}
 	return 0;
 }
+EXPORT_SYMBOL_GPL(virtio_finalize_features);
 
 static int virtio_dev_probe(struct device *_d)
 {
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index d5eb547..eac8f05 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -137,6 +137,9 @@ static inline struct virtio_device *dev_to_virtio(struct device *_dev)
 
 void virtio_break_device(struct virtio_device *dev);
 
+void virtio_config_disable(struct virtio_device *dev);
+void virtio_config_enable(struct virtio_device *dev);
+int virtio_finalize_features(struct virtio_device *dev);
 void virtio_config_changed(struct virtio_device *dev);
 #ifdef CONFIG_PM_SLEEP
 int virtio_device_freeze(struct virtio_device *dev);

Re: [net PATCH 5/5] virtio_net: XDP support for adjust_head

[Michael S. Tsirkin]

On Thu, Jan 12, 2017 at 01:45:19PM -0800, John Fastabend wrote:
> Add support for XDP adjust head by allocating a 256B header region
> that XDP programs can grow into. This is only enabled when a XDP
> program is loaded.
> 
> In order to ensure that we do not have to unwind queue headroom push
> queue setup below bpf_prog_add. It reads better to do a prog ref
> unwind vs another queue setup call.
> 
> At the moment this code must do a full reset to ensure old buffers
> without headroom on program add or with headroom on program removal
> are not used incorrectly in the datapath. Ideally we would only
> have to disable/enable the RX queues being updated but there is no
> API to do this at the moment in virtio so use the big hammer. In
> practice it is likely not that big of a problem as this will only
> happen when XDP is enabled/disabled changing programs does not
> require the reset. There is some risk that the driver may either
> have an allocation failure or for some reason fail to correctly
> negotiate with the underlying backend in this case the driver will
> be left uninitialized. I have not seen this ever happen on my test
> systems and for what its worth this same failure case can occur
> from probe and other contexts in virtio framework.

Could you explain about this a bit more?
Thanks!

> Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
> ---
>  drivers/net/virtio_net.c |  155 ++++++++++++++++++++++++++++++++++++++++------
>  drivers/virtio/virtio.c  |    9 ++-
>  include/linux/virtio.h   |    3 +
>  3 files changed, 144 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6041828..8b897e7 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -28,6 +28,7 @@
>  #include <linux/slab.h>
>  #include <linux/cpu.h>
>  #include <linux/average.h>
> +#include <linux/pci.h>
>  #include <net/busy_poll.h>
>  
>  static int napi_weight = NAPI_POLL_WEIGHT;
> @@ -159,6 +160,9 @@ struct virtnet_info {
>  	/* Ethtool settings */
>  	u8 duplex;
>  	u32 speed;
> +
> +	/* Headroom allocated in RX Queue */
> +	unsigned int headroom;
>  };
>  
>  struct padded_vnet_hdr {
> @@ -359,6 +363,7 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
>  	}
>  
>  	if (vi->mergeable_rx_bufs) {
> +		xdp->data -= sizeof(struct virtio_net_hdr_mrg_rxbuf);
>  		/* Zero header and leave csum up to XDP layers */
>  		hdr = xdp->data;
>  		memset(hdr, 0, vi->hdr_len);
> @@ -375,7 +380,9 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
>  		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);
> +		skb_to_sgvec(skb, sq->sg + 1,
> +			     xdp->data - xdp->data_hard_start,
> +			     xdp->data_end - xdp->data);
>  	}
>  	err = virtqueue_add_outbuf(sq->vq, sq->sg, num_sg,
>  				   data, GFP_ATOMIC);
> @@ -401,7 +408,6 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  	struct bpf_prog *xdp_prog;
>  
>  	len -= vi->hdr_len;
> -	skb_trim(skb, len);
>  
>  	rcu_read_lock();
>  	xdp_prog = rcu_dereference(rq->xdp_prog);
> @@ -413,11 +419,15 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
>  			goto err_xdp;
>  
> -		xdp.data = skb->data;
> +		xdp.data_hard_start = skb->data;
> +		xdp.data = skb->data + vi->headroom;
>  		xdp.data_end = xdp.data + len;
>  		act = bpf_prog_run_xdp(xdp_prog, &xdp);
>  		switch (act) {
>  		case XDP_PASS:
> +			/* Recalculate length in case bpf program changed it */
> +			len = xdp.data_end - xdp.data;
> +			__skb_pull(skb, xdp.data - xdp.data_hard_start);
>  			break;
>  		case XDP_TX:
>  			virtnet_xdp_xmit(vi, rq, &xdp, skb);
> @@ -432,6 +442,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  	}
>  	rcu_read_unlock();
>  
> +	skb_trim(skb, len);
>  	return skb;
>  
>  err_xdp:
> @@ -569,7 +580,11 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  		if (unlikely(hdr->hdr.gso_type))
>  			goto err_xdp;
>  
> +		/* Allow consuming headroom but reserve enough space to push
> +		 * the descriptor on if we get an XDP_TX return code.
> +		 */
>  		data = page_address(xdp_page) + offset;
> +		xdp.data_hard_start = data - vi->headroom + desc_room;
>  		xdp.data = data + desc_room;
>  		xdp.data_end = xdp.data + (len - vi->hdr_len);
>  		act = bpf_prog_run_xdp(xdp_prog, &xdp);
> @@ -748,20 +763,21 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>  static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>  			     gfp_t gfp)
>  {
> +	int headroom = GOOD_PACKET_LEN + vi->headroom;
>  	struct sk_buff *skb;
>  	struct virtio_net_hdr_mrg_rxbuf *hdr;
>  	int err;
>  
> -	skb = __netdev_alloc_skb_ip_align(vi->dev, GOOD_PACKET_LEN, gfp);
> +	skb = __netdev_alloc_skb_ip_align(vi->dev, headroom, gfp);
>  	if (unlikely(!skb))
>  		return -ENOMEM;
>  
> -	skb_put(skb, GOOD_PACKET_LEN);
> +	skb_put(skb, headroom);
>  
>  	hdr = skb_vnet_hdr(skb);
>  	sg_init_table(rq->sg, 2);
>  	sg_set_buf(rq->sg, hdr, vi->hdr_len);
> -	skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);
> +	skb_to_sgvec(skb, rq->sg + 1, vi->headroom, skb->len - vi->headroom);
>  
>  	err = virtqueue_add_inbuf(rq->vq, rq->sg, 2, skb, gfp);
>  	if (err < 0)
> @@ -829,24 +845,27 @@ static unsigned int get_mergeable_buf_len(struct ewma_pkt_len *avg_pkt_len)
>  	return ALIGN(len, MERGEABLE_BUFFER_ALIGN);
>  }
>  
> -static int add_recvbuf_mergeable(struct receive_queue *rq, gfp_t gfp)
> +static int add_recvbuf_mergeable(struct virtnet_info *vi,
> +				 struct receive_queue *rq, gfp_t gfp)
>  {
>  	struct page_frag *alloc_frag = &rq->alloc_frag;
> +	unsigned int headroom = vi->headroom;
>  	char *buf;
>  	unsigned long ctx;
>  	int err;
>  	unsigned int len, hole;
>  
>  	len = get_mergeable_buf_len(&rq->mrg_avg_pkt_len);
> -	if (unlikely(!skb_page_frag_refill(len, alloc_frag, gfp)))
> +	if (unlikely(!skb_page_frag_refill(len + headroom, alloc_frag, gfp)))
>  		return -ENOMEM;
>  
>  	buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> +	buf += headroom; /* advance address leaving hole at front of pkt */
>  	ctx = mergeable_buf_to_ctx(buf, len);
>  	get_page(alloc_frag->page);
> -	alloc_frag->offset += len;
> +	alloc_frag->offset += len + headroom;
>  	hole = alloc_frag->size - alloc_frag->offset;
> -	if (hole < len) {
> +	if (hole < len + headroom) {
>  		/* To avoid internal fragmentation, if there is very likely not
>  		 * enough space for another buffer, add the remaining space to
>  		 * the current buffer. This extra space is not included in
> @@ -880,7 +899,7 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
>  	gfp |= __GFP_COLD;
>  	do {
>  		if (vi->mergeable_rx_bufs)
> -			err = add_recvbuf_mergeable(rq, gfp);
> +			err = add_recvbuf_mergeable(vi, rq, gfp);
>  		else if (vi->big_packets)
>  			err = add_recvbuf_big(vi, rq, gfp);
>  		else
> @@ -1675,12 +1694,90 @@ static void virtnet_init_settings(struct net_device *dev)
>  	.set_settings = virtnet_set_settings,
>  };
>  
> +#define VIRTIO_XDP_HEADROOM 256
> +
> +static int init_vqs(struct virtnet_info *vi);
> +static void remove_vq_common(struct virtnet_info *vi, bool lock);
> +
> +/* Reset virtio device with RTNL held this is very similar to the
> + * freeze()/restore() logic except we need to ensure locking. It is
> + * possible that this routine may fail and leave the driver in a
> + * failed state. However assuming the driver negotiated correctly
> + * at probe time we _should_ be able to (re)negotiate driver again.
> + */
> +static int virtnet_xdp_reset(struct virtnet_info *vi)
> +{
> +	struct virtio_device *vdev = vi->vdev;
> +	unsigned int status;
> +	int i, ret;
> +
> +	/* Disable and unwind rings */
> +	virtio_config_disable(vdev);
> +	vdev->failed = vdev->config->get_status(vdev) & VIRTIO_CONFIG_S_FAILED;
> +
> +	netif_device_detach(vi->dev);
> +	cancel_delayed_work_sync(&vi->refill);
> +	if (netif_running(vi->dev)) {
> +		for (i = 0; i < vi->max_queue_pairs; i++)
> +			napi_disable(&vi->rq[i].napi);
> +	}
> +
> +	remove_vq_common(vi, false);
> +
> +	/* Do a reset per virtio spec recommendation */
> +	vdev->config->reset(vdev);
> +
> +	/* Acknowledge that we've seen the device. */
> +	status = vdev->config->get_status(vdev);
> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_ACKNOWLEDGE);
> +
> +	/* Notify driver is up and finalize features per specification. The
> +	 * error code from finalize features is checked here but should not
> +	 * fail because we assume features were previously synced successfully.
> +	 */
> +	status = vdev->config->get_status(vdev);
> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_DRIVER);
> +	ret = virtio_finalize_features(vdev);
> +	if (ret) {
> +		netdev_warn(vi->dev, "virtio_finalize_features failed during reset aborting\n");
> +		goto err;
> +	}
> +
> +	ret = init_vqs(vi);
> +	if (ret) {
> +		netdev_warn(vi->dev, "init_vqs failed during reset aborting\n");
> +		goto err;
> +	}
> +	virtio_device_ready(vi->vdev);
> +
> +	if (netif_running(vi->dev)) {
> +		for (i = 0; i < vi->curr_queue_pairs; i++)
> +			if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> +				schedule_delayed_work(&vi->refill, 0);
> +
> +		for (i = 0; i < vi->max_queue_pairs; i++)
> +			virtnet_napi_enable(&vi->rq[i]);
> +	}
> +	netif_device_attach(vi->dev);
> +	/* Finally, tell the device we're all set */
> +	status = vdev->config->get_status(vdev);
> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_DRIVER_OK);
> +	virtio_config_enable(vdev);
> +
> +	return 0;
> +err:
> +	status = vdev->config->get_status(vdev);
> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_FAILED);
> +	return ret;
> +}
> +
>  static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  {
>  	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	struct bpf_prog *old_prog;
>  	u16 xdp_qp = 0, curr_qp;
> +	unsigned int old_hr;
>  	int i, err;
>  
>  	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> @@ -1712,18 +1809,31 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  		return -ENOMEM;
>  	}
>  
> -	err = virtnet_set_queues(vi, curr_qp + xdp_qp);
> -	if (err) {
> -		dev_warn(&dev->dev, "XDP Device queue allocation failure.\n");
> -		return err;
> -	}
> -
> +	old_hr = vi->headroom;
>  	if (prog) {
>  		prog = bpf_prog_add(prog, vi->max_queue_pairs - 1);
> -		if (IS_ERR(prog)) {
> -			virtnet_set_queues(vi, curr_qp);
> +		if (IS_ERR(prog))
>  			return PTR_ERR(prog);
> -		}
> +		vi->headroom = VIRTIO_XDP_HEADROOM;
> +	} else {
> +		vi->headroom = 0;
> +	}
> +
> +	/* Changing the headroom in buffers is a disruptive operation because
> +	 * existing buffers must be flushed and reallocated. This will happen
> +	 * when a xdp program is initially added or xdp is disabled by removing
> +	 * the xdp program.
> +	 */
> +	if (old_hr != vi->headroom) {
> +		err = virtnet_xdp_reset(vi);
> +		if (err)
> +			goto err_reset;
> +	}
> +
> +	err = virtnet_set_queues(vi, curr_qp + xdp_qp);
> +	if (err) {
> +		dev_warn(&dev->dev, "XDP Device queue allocation failure.\n");
> +		goto err_reset;
>  	}
>  
>  	vi->xdp_queue_pairs = xdp_qp;
> @@ -1737,6 +1847,11 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  	}
>  
>  	return 0;
> +err_reset:
> +	if (prog)
> +		bpf_prog_sub(prog, vi->max_queue_pairs - 1);
> +	vi->headroom = old_hr;
> +	return err;
>  }
>  
>  static bool virtnet_xdp_query(struct net_device *dev)
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index 7062bb0..0e922b9 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -145,14 +145,15 @@ void virtio_config_changed(struct virtio_device *dev)
>  }
>  EXPORT_SYMBOL_GPL(virtio_config_changed);
>  
> -static void virtio_config_disable(struct virtio_device *dev)
> +void virtio_config_disable(struct virtio_device *dev)
>  {
>  	spin_lock_irq(&dev->config_lock);
>  	dev->config_enabled = false;
>  	spin_unlock_irq(&dev->config_lock);
>  }
> +EXPORT_SYMBOL_GPL(virtio_config_disable);
>  
> -static void virtio_config_enable(struct virtio_device *dev)
> +void virtio_config_enable(struct virtio_device *dev)
>  {
>  	spin_lock_irq(&dev->config_lock);
>  	dev->config_enabled = true;
> @@ -161,8 +162,9 @@ static void virtio_config_enable(struct virtio_device *dev)
>  	dev->config_change_pending = false;
>  	spin_unlock_irq(&dev->config_lock);
>  }
> +EXPORT_SYMBOL_GPL(virtio_config_enable);
>  
> -static int virtio_finalize_features(struct virtio_device *dev)
> +int virtio_finalize_features(struct virtio_device *dev)
>  {
>  	int ret = dev->config->finalize_features(dev);
>  	unsigned status;
> @@ -182,6 +184,7 @@ static int virtio_finalize_features(struct virtio_device *dev)
>  	}
>  	return 0;
>  }
> +EXPORT_SYMBOL_GPL(virtio_finalize_features);
>  
>  static int virtio_dev_probe(struct device *_d)
>  {
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index d5eb547..eac8f05 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -137,6 +137,9 @@ static inline struct virtio_device *dev_to_virtio(struct device *_dev)
>  
>  void virtio_break_device(struct virtio_device *dev);
>  
> +void virtio_config_disable(struct virtio_device *dev);
> +void virtio_config_enable(struct virtio_device *dev);
> +int virtio_finalize_features(struct virtio_device *dev);
>  void virtio_config_changed(struct virtio_device *dev);
>  #ifdef CONFIG_PM_SLEEP
>  int virtio_device_freeze(struct virtio_device *dev);

Re: [net PATCH 5/5] virtio_net: XDP support for adjust_head

[John Fastabend]

On 17-01-12 02:22 PM, Michael S. Tsirkin wrote:
> On Thu, Jan 12, 2017 at 01:45:19PM -0800, John Fastabend wrote:
>> Add support for XDP adjust head by allocating a 256B header region
>> that XDP programs can grow into. This is only enabled when a XDP
>> program is loaded.
>>
>> In order to ensure that we do not have to unwind queue headroom push
>> queue setup below bpf_prog_add. It reads better to do a prog ref
>> unwind vs another queue setup call.
>>
>> At the moment this code must do a full reset to ensure old buffers
>> without headroom on program add or with headroom on program removal
>> are not used incorrectly in the datapath. Ideally we would only
>> have to disable/enable the RX queues being updated but there is no
>> API to do this at the moment in virtio so use the big hammer. In
>> practice it is likely not that big of a problem as this will only
>> happen when XDP is enabled/disabled changing programs does not
>> require the reset. There is some risk that the driver may either
>> have an allocation failure or for some reason fail to correctly
>> negotiate with the underlying backend in this case the driver will
>> be left uninitialized. I have not seen this ever happen on my test
>> systems and for what its worth this same failure case can occur
>> from probe and other contexts in virtio framework.
> 
> Could you explain about this a bit more?
> Thanks!
> 

Sure. There are two existing paths and this patch adds a third one
where the driver basically goes through this reset path. First one
is on probe the other one is on the freeze/restore path.

The virtnet_freeze() path eventually free's the memory for rq/sq
(receive queues and send queues).

	virtnet_freeze()
		...
		remove_vq_common()
			...
			virtnet_dev_vqs()
				vdev->config->del_vqs()
				virtnet_free_queues <- this does a kfree


On virtnet_restore() path we then have to reallocate and reneg with
backend.

	virtnet_retore()
		...
		init_vqs()
			...
			virtnet_alloc_queues() <- alloc sq/rq
		virtnet_find_vqs()
			(allocates callbacks/names/vqs)

So the above allocs could fail and leave the device in a FAILED
state. This can happen today on probe or freeze/restore paths and
after this patch possibly on XDP load. Although as noted I have not
seen it happen in any of the above cases.

Second failure mode could happen if virtio_finalize_features() fails.
This seems unlikely because in order to probe successfully we had to
finalize the features successfully earlier. But it could I guess happen
based on return codes. Again never seen this actually happen. This is
called in probe case, freeze/restore case, and XDP now as well.

Does that help? Also I need to send a v2 to fix a spelling mistake and
to convert a 'unsigned' to 'unsigned int' per checkpatch warning. Always
better to run checkpatch before submitting vs after.

Thanks,
John

Re: [net PATCH 5/5] virtio_net: XDP support for adjust_head

[Michael S. Tsirkin]

On Thu, Jan 12, 2017 at 01:45:19PM -0800, John Fastabend wrote:
> Add support for XDP adjust head by allocating a 256B header region
> that XDP programs can grow into. This is only enabled when a XDP
> program is loaded.
> 
> In order to ensure that we do not have to unwind queue headroom push
> queue setup below bpf_prog_add. It reads better to do a prog ref
> unwind vs another queue setup call.
> 
> At the moment this code must do a full reset to ensure old buffers
> without headroom on program add or with headroom on program removal
> are not used incorrectly in the datapath. Ideally we would only
> have to disable/enable the RX queues being updated but there is no
> API to do this at the moment in virtio so use the big hammer. In
> practice it is likely not that big of a problem as this will only
> happen when XDP is enabled/disabled changing programs does not
> require the reset. There is some risk that the driver may either
> have an allocation failure or for some reason fail to correctly
> negotiate with the underlying backend in this case the driver will
> be left uninitialized. I have not seen this ever happen on my test
> systems and for what its worth this same failure case can occur
> from probe and other contexts in virtio framework.
> 
> Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
> ---
>  drivers/net/virtio_net.c |  155 ++++++++++++++++++++++++++++++++++++++++------
>  drivers/virtio/virtio.c  |    9 ++-
>  include/linux/virtio.h   |    3 +
>  3 files changed, 144 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6041828..8b897e7 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -28,6 +28,7 @@
>  #include <linux/slab.h>
>  #include <linux/cpu.h>
>  #include <linux/average.h>
> +#include <linux/pci.h>
>  #include <net/busy_poll.h>
>  
>  static int napi_weight = NAPI_POLL_WEIGHT;
> @@ -159,6 +160,9 @@ struct virtnet_info {
>  	/* Ethtool settings */
>  	u8 duplex;
>  	u32 speed;
> +
> +	/* Headroom allocated in RX Queue */
> +	unsigned int headroom;
>  };
>  
>  struct padded_vnet_hdr {
> @@ -359,6 +363,7 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
>  	}
>  
>  	if (vi->mergeable_rx_bufs) {
> +		xdp->data -= sizeof(struct virtio_net_hdr_mrg_rxbuf);
>  		/* Zero header and leave csum up to XDP layers */
>  		hdr = xdp->data;
>  		memset(hdr, 0, vi->hdr_len);
> @@ -375,7 +380,9 @@ static void virtnet_xdp_xmit(struct virtnet_info *vi,
>  		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);
> +		skb_to_sgvec(skb, sq->sg + 1,
> +			     xdp->data - xdp->data_hard_start,
> +			     xdp->data_end - xdp->data);
>  	}
>  	err = virtqueue_add_outbuf(sq->vq, sq->sg, num_sg,
>  				   data, GFP_ATOMIC);
> @@ -401,7 +408,6 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  	struct bpf_prog *xdp_prog;
>  
>  	len -= vi->hdr_len;
> -	skb_trim(skb, len);
>  
>  	rcu_read_lock();
>  	xdp_prog = rcu_dereference(rq->xdp_prog);
> @@ -413,11 +419,15 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
>  			goto err_xdp;
>  
> -		xdp.data = skb->data;
> +		xdp.data_hard_start = skb->data;
> +		xdp.data = skb->data + vi->headroom;
>  		xdp.data_end = xdp.data + len;
>  		act = bpf_prog_run_xdp(xdp_prog, &xdp);
>  		switch (act) {
>  		case XDP_PASS:
> +			/* Recalculate length in case bpf program changed it */
> +			len = xdp.data_end - xdp.data;
> +			__skb_pull(skb, xdp.data - xdp.data_hard_start);
>  			break;
>  		case XDP_TX:
>  			virtnet_xdp_xmit(vi, rq, &xdp, skb);
> @@ -432,6 +442,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  	}
>  	rcu_read_unlock();
>  
> +	skb_trim(skb, len);
>  	return skb;
>  
>  err_xdp:
> @@ -569,7 +580,11 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  		if (unlikely(hdr->hdr.gso_type))
>  			goto err_xdp;
>  
> +		/* Allow consuming headroom but reserve enough space to push
> +		 * the descriptor on if we get an XDP_TX return code.
> +		 */
>  		data = page_address(xdp_page) + offset;
> +		xdp.data_hard_start = data - vi->headroom + desc_room;
>  		xdp.data = data + desc_room;
>  		xdp.data_end = xdp.data + (len - vi->hdr_len);
>  		act = bpf_prog_run_xdp(xdp_prog, &xdp);
> @@ -748,20 +763,21 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>  static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>  			     gfp_t gfp)
>  {
> +	int headroom = GOOD_PACKET_LEN + vi->headroom;
>  	struct sk_buff *skb;
>  	struct virtio_net_hdr_mrg_rxbuf *hdr;
>  	int err;
>  
> -	skb = __netdev_alloc_skb_ip_align(vi->dev, GOOD_PACKET_LEN, gfp);
> +	skb = __netdev_alloc_skb_ip_align(vi->dev, headroom, gfp);
>  	if (unlikely(!skb))
>  		return -ENOMEM;
>  
> -	skb_put(skb, GOOD_PACKET_LEN);
> +	skb_put(skb, headroom);
>  
>  	hdr = skb_vnet_hdr(skb);
>  	sg_init_table(rq->sg, 2);
>  	sg_set_buf(rq->sg, hdr, vi->hdr_len);
> -	skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);
> +	skb_to_sgvec(skb, rq->sg + 1, vi->headroom, skb->len - vi->headroom);
>  
>  	err = virtqueue_add_inbuf(rq->vq, rq->sg, 2, skb, gfp);
>  	if (err < 0)
> @@ -829,24 +845,27 @@ static unsigned int get_mergeable_buf_len(struct ewma_pkt_len *avg_pkt_len)
>  	return ALIGN(len, MERGEABLE_BUFFER_ALIGN);
>  }
>  
> -static int add_recvbuf_mergeable(struct receive_queue *rq, gfp_t gfp)
> +static int add_recvbuf_mergeable(struct virtnet_info *vi,
> +				 struct receive_queue *rq, gfp_t gfp)
>  {
>  	struct page_frag *alloc_frag = &rq->alloc_frag;
> +	unsigned int headroom = vi->headroom;
>  	char *buf;
>  	unsigned long ctx;
>  	int err;
>  	unsigned int len, hole;
>  
>  	len = get_mergeable_buf_len(&rq->mrg_avg_pkt_len);
> -	if (unlikely(!skb_page_frag_refill(len, alloc_frag, gfp)))
> +	if (unlikely(!skb_page_frag_refill(len + headroom, alloc_frag, gfp)))
>  		return -ENOMEM;
>  
>  	buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> +	buf += headroom; /* advance address leaving hole at front of pkt */
>  	ctx = mergeable_buf_to_ctx(buf, len);
>  	get_page(alloc_frag->page);
> -	alloc_frag->offset += len;
> +	alloc_frag->offset += len + headroom;
>  	hole = alloc_frag->size - alloc_frag->offset;
> -	if (hole < len) {
> +	if (hole < len + headroom) {
>  		/* To avoid internal fragmentation, if there is very likely not
>  		 * enough space for another buffer, add the remaining space to
>  		 * the current buffer. This extra space is not included in
> @@ -880,7 +899,7 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
>  	gfp |= __GFP_COLD;
>  	do {
>  		if (vi->mergeable_rx_bufs)
> -			err = add_recvbuf_mergeable(rq, gfp);
> +			err = add_recvbuf_mergeable(vi, rq, gfp);
>  		else if (vi->big_packets)
>  			err = add_recvbuf_big(vi, rq, gfp);
>  		else
> @@ -1675,12 +1694,90 @@ static void virtnet_init_settings(struct net_device *dev)
>  	.set_settings = virtnet_set_settings,
>  };
>  
> +#define VIRTIO_XDP_HEADROOM 256
> +
> +static int init_vqs(struct virtnet_info *vi);
> +static void remove_vq_common(struct virtnet_info *vi, bool lock);
> +
> +/* Reset virtio device with RTNL held this is very similar to the
> + * freeze()/restore() logic except we need to ensure locking. It is
> + * possible that this routine may fail and leave the driver in a
> + * failed state. However assuming the driver negotiated correctly
> + * at probe time we _should_ be able to (re)negotiate driver again.
> + */
> +static int virtnet_xdp_reset(struct virtnet_info *vi)
> +{
> +	struct virtio_device *vdev = vi->vdev;
> +	unsigned int status;
> +	int i, ret;
> +
> +	/* Disable and unwind rings */
> +	virtio_config_disable(vdev);
> +	vdev->failed = vdev->config->get_status(vdev) & VIRTIO_CONFIG_S_FAILED;
> +
> +	netif_device_detach(vi->dev);

After this point, netif_device_present
will return false, and then we have a bunch of code
that does
                if (!netif_device_present(dev))
                        return -ENODEV;


so we need to audit this code to make sure it's
all called under rtnl, correct?

We don't want it to fail because of timing.

Maybe add an assert there.


> +	cancel_delayed_work_sync(&vi->refill);
> +	if (netif_running(vi->dev)) {
> +		for (i = 0; i < vi->max_queue_pairs; i++)
> +			napi_disable(&vi->rq[i].napi);
> +	}
> +
> +	remove_vq_common(vi, false);
> +
> +	/* Do a reset per virtio spec recommendation */
> +	vdev->config->reset(vdev);
> +
> +	/* Acknowledge that we've seen the device. */
> +	status = vdev->config->get_status(vdev);
> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_ACKNOWLEDGE);
> +
> +	/* Notify driver is up and finalize features per specification. The
> +	 * error code from finalize features is checked here but should not
> +	 * fail because we assume features were previously synced successfully.
> +	 */
> +	status = vdev->config->get_status(vdev);
> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_DRIVER);
> +	ret = virtio_finalize_features(vdev);

I'd rather we put all this in virtio core, maybe call it virtio_reset or
something.

> +	if (ret) {
> +		netdev_warn(vi->dev, "virtio_finalize_features failed during reset aborting\n");
> +		goto err;
> +	}
> +
> +	ret = init_vqs(vi);
> +	if (ret) {
> +		netdev_warn(vi->dev, "init_vqs failed during reset aborting\n");
> +		goto err;
> +	}
> +	virtio_device_ready(vi->vdev);
> +
> +	if (netif_running(vi->dev)) {
> +		for (i = 0; i < vi->curr_queue_pairs; i++)
> +			if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> +				schedule_delayed_work(&vi->refill, 0);
> +
> +		for (i = 0; i < vi->max_queue_pairs; i++)
> +			virtnet_napi_enable(&vi->rq[i]);
> +	}
> +	netif_device_attach(vi->dev);
> +	/* Finally, tell the device we're all set */
> +	status = vdev->config->get_status(vdev);
> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_DRIVER_OK);
> +	virtio_config_enable(vdev);
> +
> +	return 0;
> +err:
> +	status = vdev->config->get_status(vdev);
> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_FAILED);

And maybe virtio_fail ?

> +	return ret;
> +}
> +
>  static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  {
>  	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	struct bpf_prog *old_prog;
>  	u16 xdp_qp = 0, curr_qp;
> +	unsigned int old_hr;
>  	int i, err;
>  
>  	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> @@ -1712,18 +1809,31 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  		return -ENOMEM;
>  	}
>  
> -	err = virtnet_set_queues(vi, curr_qp + xdp_qp);
> -	if (err) {
> -		dev_warn(&dev->dev, "XDP Device queue allocation failure.\n");
> -		return err;
> -	}
> -
> +	old_hr = vi->headroom;
>  	if (prog) {
>  		prog = bpf_prog_add(prog, vi->max_queue_pairs - 1);
> -		if (IS_ERR(prog)) {
> -			virtnet_set_queues(vi, curr_qp);
> +		if (IS_ERR(prog))
>  			return PTR_ERR(prog);
> -		}
> +		vi->headroom = VIRTIO_XDP_HEADROOM;
> +	} else {
> +		vi->headroom = 0;
> +	}
> +
> +	/* Changing the headroom in buffers is a disruptive operation because
> +	 * existing buffers must be flushed and reallocated. This will happen
> +	 * when a xdp program is initially added or xdp is disabled by removing
> +	 * the xdp program.
> +	 */
> +	if (old_hr != vi->headroom) {
> +		err = virtnet_xdp_reset(vi);
> +		if (err)
> +			goto err_reset;
> +	}
> +
> +	err = virtnet_set_queues(vi, curr_qp + xdp_qp);
> +	if (err) {
> +		dev_warn(&dev->dev, "XDP Device queue allocation failure.\n");
> +		goto err_reset;
>  	}
>  
>  	vi->xdp_queue_pairs = xdp_qp;
> @@ -1737,6 +1847,11 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  	}
>  
>  	return 0;
> +err_reset:
> +	if (prog)
> +		bpf_prog_sub(prog, vi->max_queue_pairs - 1);
> +	vi->headroom = old_hr;
> +	return err;
>  }
>  
>  static bool virtnet_xdp_query(struct net_device *dev)
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index 7062bb0..0e922b9 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -145,14 +145,15 @@ void virtio_config_changed(struct virtio_device *dev)
>  }
>  EXPORT_SYMBOL_GPL(virtio_config_changed);
>  
> -static void virtio_config_disable(struct virtio_device *dev)
> +void virtio_config_disable(struct virtio_device *dev)
>  {
>  	spin_lock_irq(&dev->config_lock);
>  	dev->config_enabled = false;
>  	spin_unlock_irq(&dev->config_lock);
>  }
> +EXPORT_SYMBOL_GPL(virtio_config_disable);
>  
> -static void virtio_config_enable(struct virtio_device *dev)
> +void virtio_config_enable(struct virtio_device *dev)
>  {
>  	spin_lock_irq(&dev->config_lock);
>  	dev->config_enabled = true;
> @@ -161,8 +162,9 @@ static void virtio_config_enable(struct virtio_device *dev)
>  	dev->config_change_pending = false;
>  	spin_unlock_irq(&dev->config_lock);
>  }
> +EXPORT_SYMBOL_GPL(virtio_config_enable);
>  
> -static int virtio_finalize_features(struct virtio_device *dev)
> +int virtio_finalize_features(struct virtio_device *dev)
>  {
>  	int ret = dev->config->finalize_features(dev);
>  	unsigned status;
> @@ -182,6 +184,7 @@ static int virtio_finalize_features(struct virtio_device *dev)
>  	}
>  	return 0;
>  }
> +EXPORT_SYMBOL_GPL(virtio_finalize_features);
>  
>  static int virtio_dev_probe(struct device *_d)
>  {
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index d5eb547..eac8f05 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -137,6 +137,9 @@ static inline struct virtio_device *dev_to_virtio(struct device *_dev)
>  
>  void virtio_break_device(struct virtio_device *dev);
>  
> +void virtio_config_disable(struct virtio_device *dev);
> +void virtio_config_enable(struct virtio_device *dev);
> +int virtio_finalize_features(struct virtio_device *dev);
>  void virtio_config_changed(struct virtio_device *dev);
>  #ifdef CONFIG_PM_SLEEP
>  int virtio_device_freeze(struct virtio_device *dev);

Re: [net PATCH 5/5] virtio_net: XDP support for adjust_head

[John Fastabend]

On 17-01-13 09:23 AM, Michael S. Tsirkin wrote:
> On Thu, Jan 12, 2017 at 01:45:19PM -0800, John Fastabend wrote:
>> Add support for XDP adjust head by allocating a 256B header region
>> that XDP programs can grow into. This is only enabled when a XDP
>> program is loaded.
>>
>> In order to ensure that we do not have to unwind queue headroom push
>> queue setup below bpf_prog_add. It reads better to do a prog ref
>> unwind vs another queue setup call.
>>
>> At the moment this code must do a full reset to ensure old buffers
>> without headroom on program add or with headroom on program removal
>> are not used incorrectly in the datapath. Ideally we would only
>> have to disable/enable the RX queues being updated but there is no
>> API to do this at the moment in virtio so use the big hammer. In
>> practice it is likely not that big of a problem as this will only
>> happen when XDP is enabled/disabled changing programs does not
>> require the reset. There is some risk that the driver may either
>> have an allocation failure or for some reason fail to correctly
>> negotiate with the underlying backend in this case the driver will
>> be left uninitialized. I have not seen this ever happen on my test
>> systems and for what its worth this same failure case can occur
>> from probe and other contexts in virtio framework.
>>
>> Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
>> ---


[...]

>>  
>> +#define VIRTIO_XDP_HEADROOM 256
>> +
>> +static int init_vqs(struct virtnet_info *vi);
>> +static void remove_vq_common(struct virtnet_info *vi, bool lock);
>> +
>> +/* Reset virtio device with RTNL held this is very similar to the
>> + * freeze()/restore() logic except we need to ensure locking. It is
>> + * possible that this routine may fail and leave the driver in a
>> + * failed state. However assuming the driver negotiated correctly
>> + * at probe time we _should_ be able to (re)negotiate driver again.
>> + */
>> +static int virtnet_xdp_reset(struct virtnet_info *vi)
>> +{
>> +	struct virtio_device *vdev = vi->vdev;
>> +	unsigned int status;
>> +	int i, ret;
>> +
>> +	/* Disable and unwind rings */
>> +	virtio_config_disable(vdev);
>> +	vdev->failed = vdev->config->get_status(vdev) & VIRTIO_CONFIG_S_FAILED;
>> +
>> +	netif_device_detach(vi->dev);
> 
> After this point, netif_device_present
> will return false, and then we have a bunch of code
> that does
>                 if (!netif_device_present(dev))
>                         return -ENODEV;
> 
> 
> so we need to audit this code to make sure it's
> all called under rtnl, correct?
> 

Correct. In the XDP case it is.

> We don't want it to fail because of timing.
> 
> Maybe add an assert there.
> 

I can add an assert here to ensure it doesn't ever get
refactored out or something.

> 
>> +	cancel_delayed_work_sync(&vi->refill);
>> +	if (netif_running(vi->dev)) {
>> +		for (i = 0; i < vi->max_queue_pairs; i++)
>> +			napi_disable(&vi->rq[i].napi);
>> +	}
>> +
>> +	remove_vq_common(vi, false);
>> +
>> +	/* Do a reset per virtio spec recommendation */
>> +	vdev->config->reset(vdev);
>> +
>> +	/* Acknowledge that we've seen the device. */
>> +	status = vdev->config->get_status(vdev);
>> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_ACKNOWLEDGE);
>> +
>> +	/* Notify driver is up and finalize features per specification. The
>> +	 * error code from finalize features is checked here but should not
>> +	 * fail because we assume features were previously synced successfully.
>> +	 */
>> +	status = vdev->config->get_status(vdev);
>> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_DRIVER);
>> +	ret = virtio_finalize_features(vdev);
> 
> I'd rather we put all this in virtio core, maybe call it virtio_reset or
> something.

At first I started to do this but decided it was easier to open code it I
was on the fence though so if we think it would be cleaner then I will
do it.

The trick is needs to be broken down into two pieces, something like the
following,

	virtio_reset() {
		do_generic_down_part  -> pci pieces
		vdev->config->down()  -> do down part of device specifics
		do_generic_up_part
		vdev->config->up()    -> do up part of device specifics
		do_finalize_part
	}

Alternatively we could reuse the freeze/restore device callbacks but those
make assumptions about locking. So we could pass a context through but per
Stephen's comment that gets a bit fragile. And sparse doesn't like it either
apparently. I think making it an explicit down/up reset callback might
make it clean and reusable for any other devices.

Any thoughts? My preference outside of open coding it is the new down_reset
and up_reset callbacks.

> 
>> +	if (ret) {
>> +		netdev_warn(vi->dev, "virtio_finalize_features failed during reset aborting\n");
>> +		goto err;
>> +	}
>> +
>> +	ret = init_vqs(vi);
>> +	if (ret) {
>> +		netdev_warn(vi->dev, "init_vqs failed during reset aborting\n");
>> +		goto err;
>> +	}
>> +	virtio_device_ready(vi->vdev);
>> +
>> +	if (netif_running(vi->dev)) {
>> +		for (i = 0; i < vi->curr_queue_pairs; i++)
>> +			if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
>> +				schedule_delayed_work(&vi->refill, 0);
>> +
>> +		for (i = 0; i < vi->max_queue_pairs; i++)
>> +			virtnet_napi_enable(&vi->rq[i]);
>> +	}
>> +	netif_device_attach(vi->dev);
>> +	/* Finally, tell the device we're all set */
>> +	status = vdev->config->get_status(vdev);
>> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_DRIVER_OK);
>> +	virtio_config_enable(vdev);
>> +
>> +	return 0;
>> +err:
>> +	status = vdev->config->get_status(vdev);
>> +	vdev->config->set_status(vdev, status | VIRTIO_CONFIG_S_FAILED);
> 
> And maybe virtio_fail ?
> 

Sure.

Thanks,
John