[PATCH net-next v5 1/2] net: mhi-net: Add re-aggregation of fragmented packets

[PATCH net-next v5 1/2] net: mhi-net: Add re-aggregation of fragmented packets

[Loic Poulain]

When device side MTU is larger than host side MTU, the packets
(typically rmnet packets) are split over multiple MHI transfers.
In that case, fragments must be re-aggregated to recover the packet
before forwarding to upper layer.

A fragmented packet result in -EOVERFLOW MHI transaction status for
each of its fragments, except the final one. Such transfer was
previously considered as error and fragments were simply dropped.

This change adds re-aggregation mechanism using skb chaining, via
skb frag_list.

A warning (once) is printed since this behavior usually comes from
a misconfiguration of the device (e.g. modem MTU).

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
---
 v2: use zero-copy skb chaining instead of skb_copy_expand.
 v3: Fix nit in commit msg + remove misleading inline comment for frag_list
 v4: no change
 v5: reword/fix commit subject

 drivers/net/mhi_net.c | 74 ++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 64 insertions(+), 10 deletions(-)

diff --git a/drivers/net/mhi_net.c b/drivers/net/mhi_net.c
index 4f512531..8800991 100644
--- a/drivers/net/mhi_net.c
+++ b/drivers/net/mhi_net.c
@@ -32,6 +32,8 @@ struct mhi_net_stats {
 struct mhi_net_dev {
 	struct mhi_device *mdev;
 	struct net_device *ndev;
+	struct sk_buff *skbagg_head;
+	struct sk_buff *skbagg_tail;
 	struct delayed_work rx_refill;
 	struct mhi_net_stats stats;
 	u32 rx_queue_sz;
@@ -132,6 +134,32 @@ static void mhi_net_setup(struct net_device *ndev)
 	ndev->tx_queue_len = 1000;
 }
 
+static struct sk_buff *mhi_net_skb_agg(struct mhi_net_dev *mhi_netdev,
+				       struct sk_buff *skb)
+{
+	struct sk_buff *head = mhi_netdev->skbagg_head;
+	struct sk_buff *tail = mhi_netdev->skbagg_tail;
+
+	/* This is non-paged skb chaining using frag_list */
+	if (!head) {
+		mhi_netdev->skbagg_head = skb;
+		return skb;
+	}
+
+	if (!skb_shinfo(head)->frag_list)
+		skb_shinfo(head)->frag_list = skb;
+	else
+		tail->next = skb;
+
+	head->len += skb->len;
+	head->data_len += skb->len;
+	head->truesize += skb->truesize;
+
+	mhi_netdev->skbagg_tail = skb;
+
+	return mhi_netdev->skbagg_head;
+}
+
 static void mhi_net_dl_callback(struct mhi_device *mhi_dev,
 				struct mhi_result *mhi_res)
 {
@@ -142,19 +170,42 @@ static void mhi_net_dl_callback(struct mhi_device *mhi_dev,
 	free_desc_count = mhi_get_free_desc_count(mhi_dev, DMA_FROM_DEVICE);
 
 	if (unlikely(mhi_res->transaction_status)) {
-		dev_kfree_skb_any(skb);
-
-		/* MHI layer stopping/resetting the DL channel */
-		if (mhi_res->transaction_status == -ENOTCONN)
+		switch (mhi_res->transaction_status) {
+		case -EOVERFLOW:
+			/* Packet can not fit in one MHI buffer and has been
+			 * split over multiple MHI transfers, do re-aggregation.
+			 * That usually means the device side MTU is larger than
+			 * the host side MTU/MRU. Since this is not optimal,
+			 * print a warning (once).
+			 */
+			netdev_warn_once(mhi_netdev->ndev,
+					 "Fragmented packets received, fix MTU?\n");
+			skb_put(skb, mhi_res->bytes_xferd);
+			mhi_net_skb_agg(mhi_netdev, skb);
+			break;
+		case -ENOTCONN:
+			/* MHI layer stopping/resetting the DL channel */
+			dev_kfree_skb_any(skb);
 			return;
-
-		u64_stats_update_begin(&mhi_netdev->stats.rx_syncp);
-		u64_stats_inc(&mhi_netdev->stats.rx_errors);
-		u64_stats_update_end(&mhi_netdev->stats.rx_syncp);
+		default:
+			/* Unknown error, simply drop */
+			dev_kfree_skb_any(skb);
+			u64_stats_update_begin(&mhi_netdev->stats.rx_syncp);
+			u64_stats_inc(&mhi_netdev->stats.rx_errors);
+			u64_stats_update_end(&mhi_netdev->stats.rx_syncp);
+		}
 	} else {
+		skb_put(skb, mhi_res->bytes_xferd);
+
+		if (mhi_netdev->skbagg_head) {
+			/* Aggregate the final fragment */
+			skb = mhi_net_skb_agg(mhi_netdev, skb);
+			mhi_netdev->skbagg_head = NULL;
+		}
+
 		u64_stats_update_begin(&mhi_netdev->stats.rx_syncp);
 		u64_stats_inc(&mhi_netdev->stats.rx_packets);
-		u64_stats_add(&mhi_netdev->stats.rx_bytes, mhi_res->bytes_xferd);
+		u64_stats_add(&mhi_netdev->stats.rx_bytes, skb->len);
 		u64_stats_update_end(&mhi_netdev->stats.rx_syncp);
 
 		switch (skb->data[0] & 0xf0) {
@@ -169,7 +220,6 @@ static void mhi_net_dl_callback(struct mhi_device *mhi_dev,
 			break;
 		}
 
-		skb_put(skb, mhi_res->bytes_xferd);
 		netif_rx(skb);
 	}
 
@@ -267,6 +317,7 @@ static int mhi_net_probe(struct mhi_device *mhi_dev,
 	dev_set_drvdata(dev, mhi_netdev);
 	mhi_netdev->ndev = ndev;
 	mhi_netdev->mdev = mhi_dev;
+	mhi_netdev->skbagg_head = NULL;
 	SET_NETDEV_DEV(ndev, &mhi_dev->dev);
 	SET_NETDEV_DEVTYPE(ndev, &wwan_type);
 
@@ -301,6 +352,9 @@ static void mhi_net_remove(struct mhi_device *mhi_dev)
 
 	mhi_unprepare_from_transfer(mhi_netdev->mdev);
 
+	if (mhi_netdev->skbagg_head)
+		kfree_skb(mhi_netdev->skbagg_head);
+
 	free_netdev(mhi_netdev->ndev);
 }
 
-- 
2.7.4

[PATCH net-next v5 2/2] net: qualcomm: rmnet: Fix rx_handler for non-linear skbs

[Loic Poulain]

There is no guarantee that rmnet rx_handler is only fed with linear
skbs, but current rmnet implementation does not check that, leading
to crash in case of non linear skbs processed as linear ones.

Fix that by ensuring skb linearization before processing.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Acked-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
---
 v2: Add this patch to the series to prevent crash
 v3: no change
 v4: Fix skb leak in case of skb_linearize failure
 v5: no change

 drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
index 3d7d3ab..3d00b32 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
@@ -183,6 +183,11 @@ rx_handler_result_t rmnet_rx_handler(struct sk_buff **pskb)
 	if (!skb)
 		goto done;
 
+	if (skb_linearize(skb)) {
+		kfree_skb(skb);
+		goto done;
+	}
+
 	if (skb->pkt_type == PACKET_LOOPBACK)
 		return RX_HANDLER_PASS;
 
-- 
2.7.4

Re: [PATCH net-next v5 1/2] net: mhi-net: Add re-aggregation of fragmented packets

[Jesse Brandeburg]

Loic Poulain wrote:

> When device side MTU is larger than host side MTU, the packets
> (typically rmnet packets) are split over multiple MHI transfers.
> In that case, fragments must be re-aggregated to recover the packet
> before forwarding to upper layer.
> 
> A fragmented packet result in -EOVERFLOW MHI transaction status for
> each of its fragments, except the final one. Such transfer was
> previously considered as error and fragments were simply dropped.
> 
> This change adds re-aggregation mechanism using skb chaining, via
> skb frag_list.
> 
> A warning (once) is printed since this behavior usually comes from
> a misconfiguration of the device (e.g. modem MTU).
> 
> Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
> ---
>  v2: use zero-copy skb chaining instead of skb_copy_expand.
>  v3: Fix nit in commit msg + remove misleading inline comment for frag_list
>  v4: no change
>  v5: reword/fix commit subject
> 

Acked-by: Jesse Brandeburg <jesse.brandeburg@intel.com>

Re: [PATCH net-next v5 1/2] net: mhi-net: Add re-aggregation of fragmented packets

[Jakub Kicinski]

On Thu,  4 Feb 2021 09:40:00 +0100 Loic Poulain wrote:
> When device side MTU is larger than host side MTU, the packets
> (typically rmnet packets) are split over multiple MHI transfers.
> In that case, fragments must be re-aggregated to recover the packet
> before forwarding to upper layer.
> 
> A fragmented packet result in -EOVERFLOW MHI transaction status for
> each of its fragments, except the final one. Such transfer was
> previously considered as error and fragments were simply dropped.
> 
> This change adds re-aggregation mechanism using skb chaining, via
> skb frag_list.
> 
> A warning (once) is printed since this behavior usually comes from
> a misconfiguration of the device (e.g. modem MTU).
> 
> Signed-off-by: Loic Poulain <loic.poulain@linaro.org>

Applied, thanks, but I had to invert the order of the patches.
Otherwise during bisection someone may hit a point in the tree
where mhi_net generates fragmented skbs but rmnet does not handle
them.