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Date:   Thu, 12 May 2022 01:40:23 -0700
From:   Saeed Mahameed <saeedm@...dia.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        Alexander Duyck <alexanderduyck@...com>,
        Coco Li <lixiaoyan@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Leon Romanovsky <leon@...nel.org>
Subject: Re: [PATCH v6 net-next 13/13] mlx5: support BIG TCP packets

On 09 May 20:32, Eric Dumazet wrote:
>From: Coco Li <lixiaoyan@...gle.com>
>
>mlx5 supports LSOv2.
>
>IPv6 gro/tcp stacks insert a temporary Hop-by-Hop header
>with JUMBO TLV for big packets.
>
>We need to ignore/skip this HBH header when populating TX descriptor.
>

Sorry i didn't go through all the documentations or previous discussions,
please bare with me, so why not clear HBH just before calling the
driver xmit ndo ? 

Or if HBH has to stick, why not provide some helpers to the driver, to make
it less intrusive to the driver. 

mlx5_xmit_skb() {
    skb_remove_hbh(skb);
    populate tx descriptor as usual;
    skb_restore_hbh(skb); //must be before doorbell
    ring doorbell
}

>Note that ipv6_has_hopopt_jumbo() only recognizes very specific packet
>layout, thus mlx5e_sq_xmit_wqe() is taking care of this layout only.
>
>v2: clear hopbyhop in mlx5e_tx_get_gso_ihs()
>v4: fix compile error for CONFIG_MLX5_CORE_IPOIB=y
>
>Signed-off-by: Coco Li <lixiaoyan@...gle.com>
>Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>Reviewed-by: Tariq Toukan <tariqt@...dia.com>
>Cc: Saeed Mahameed <saeedm@...dia.com>
>Cc: Leon Romanovsky <leon@...nel.org>
>---
> .../net/ethernet/mellanox/mlx5/core/en_main.c |  1 +
> .../net/ethernet/mellanox/mlx5/core/en_tx.c   | 84 +++++++++++++++----
> 2 files changed, 69 insertions(+), 16 deletions(-)
>
>diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>index d27986869b8ba070d1a4f8bcdc7e14ab54ae984e..bf3bca79e160124abd128ac1e9910cb2f39a39ff 100644
>--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>@@ -4920,6 +4920,7 @@ static void mlx5e_build_nic_netdev(struct net_device *netdev)
>
> 	netdev->priv_flags       |= IFF_UNICAST_FLT;
>
>+	netif_set_tso_max_size(netdev, GSO_MAX_SIZE);
> 	mlx5e_set_netdev_dev_addr(netdev);
> 	mlx5e_ipsec_build_netdev(priv);
> 	mlx5e_ktls_build_netdev(priv);
>diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
>index 2dc48406cd08d21ff94f665cd61ab9227f351215..b4fc45ba1b347fb9ad0f46b9c091cc45e4d3d84f 100644
>--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
>+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
>@@ -40,6 +40,7 @@
> #include "en_accel/en_accel.h"
> #include "en_accel/ipsec_rxtx.h"
> #include "en/ptp.h"
>+#include <net/ipv6.h>
>
> static void mlx5e_dma_unmap_wqe_err(struct mlx5e_txqsq *sq, u8 num_dma)
> {
>@@ -130,23 +131,32 @@ mlx5e_txwqe_build_eseg_csum(struct mlx5e_txqsq *sq, struct sk_buff *skb,
> 		sq->stats->csum_none++;
> }
>
>+/* Returns the number of header bytes that we plan
>+ * to inline later in the transmit descriptor
>+ */
> static inline u16
>-mlx5e_tx_get_gso_ihs(struct mlx5e_txqsq *sq, struct sk_buff *skb)
>+mlx5e_tx_get_gso_ihs(struct mlx5e_txqsq *sq, struct sk_buff *skb, int *hopbyhop)
> {
> 	struct mlx5e_sq_stats *stats = sq->stats;
> 	u16 ihs;
>
>+	*hopbyhop = 0;
> 	if (skb->encapsulation) {
> 		ihs = skb_inner_transport_offset(skb) + inner_tcp_hdrlen(skb);
> 		stats->tso_inner_packets++;
> 		stats->tso_inner_bytes += skb->len - ihs;
> 	} else {
>-		if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
>+		if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) {
> 			ihs = skb_transport_offset(skb) + sizeof(struct udphdr);
>-		else
>+		} else {
> 			ihs = skb_transport_offset(skb) + tcp_hdrlen(skb);
>+			if (ipv6_has_hopopt_jumbo(skb)) {
>+				*hopbyhop = sizeof(struct hop_jumbo_hdr);
>+				ihs -= sizeof(struct hop_jumbo_hdr);
>+			}
>+		}
> 		stats->tso_packets++;
>-		stats->tso_bytes += skb->len - ihs;
>+		stats->tso_bytes += skb->len - ihs - *hopbyhop;
> 	}
>
> 	return ihs;
>@@ -208,6 +218,7 @@ struct mlx5e_tx_attr {
> 	__be16 mss;
> 	u16 insz;
> 	u8 opcode;
>+	u8 hopbyhop;
> };
>
> struct mlx5e_tx_wqe_attr {
>@@ -244,14 +255,16 @@ static void mlx5e_sq_xmit_prepare(struct mlx5e_txqsq *sq, struct sk_buff *skb,
> 	struct mlx5e_sq_stats *stats = sq->stats;
>
> 	if (skb_is_gso(skb)) {
>-		u16 ihs = mlx5e_tx_get_gso_ihs(sq, skb);
>+		int hopbyhop;
>+		u16 ihs = mlx5e_tx_get_gso_ihs(sq, skb, &hopbyhop);
>
> 		*attr = (struct mlx5e_tx_attr) {
> 			.opcode    = MLX5_OPCODE_LSO,
> 			.mss       = cpu_to_be16(skb_shinfo(skb)->gso_size),
> 			.ihs       = ihs,
> 			.num_bytes = skb->len + (skb_shinfo(skb)->gso_segs - 1) * ihs,
>-			.headlen   = skb_headlen(skb) - ihs,
>+			.headlen   = skb_headlen(skb) - ihs - hopbyhop,
>+			.hopbyhop  = hopbyhop,
> 		};
>
> 		stats->packets += skb_shinfo(skb)->gso_segs;
>@@ -365,7 +378,8 @@ mlx5e_sq_xmit_wqe(struct mlx5e_txqsq *sq, struct sk_buff *skb,
> 	struct mlx5_wqe_eth_seg  *eseg;
> 	struct mlx5_wqe_data_seg *dseg;
> 	struct mlx5e_tx_wqe_info *wi;
>-
>+	u16 ihs = attr->ihs;
>+	struct ipv6hdr *h6;
> 	struct mlx5e_sq_stats *stats = sq->stats;
> 	int num_dma;
>
>@@ -379,15 +393,36 @@ mlx5e_sq_xmit_wqe(struct mlx5e_txqsq *sq, struct sk_buff *skb,
>
> 	eseg->mss = attr->mss;
>
>-	if (attr->ihs) {
>-		if (skb_vlan_tag_present(skb)) {
>-			eseg->inline_hdr.sz |= cpu_to_be16(attr->ihs + VLAN_HLEN);
>-			mlx5e_insert_vlan(eseg->inline_hdr.start, skb, attr->ihs);
>+	if (ihs) {
>+		u8 *start = eseg->inline_hdr.start;
>+
>+		if (unlikely(attr->hopbyhop)) {
>+			/* remove the HBH header.
>+			 * Layout: [Ethernet header][IPv6 header][HBH][TCP header]
>+			 */
>+			if (skb_vlan_tag_present(skb)) {
>+				mlx5e_insert_vlan(start, skb, ETH_HLEN + sizeof(*h6));
>+				ihs += VLAN_HLEN;
>+				h6 = (struct ipv6hdr *)(start + sizeof(struct vlan_ethhdr));
>+			} else {
>+				memcpy(start, skb->data, ETH_HLEN + sizeof(*h6));
>+				h6 = (struct ipv6hdr *)(start + ETH_HLEN);
>+			}
>+			h6->nexthdr = IPPROTO_TCP;
>+			/* Copy the TCP header after the IPv6 one */
>+			memcpy(h6 + 1,
>+			       skb->data + ETH_HLEN + sizeof(*h6) +
>+					sizeof(struct hop_jumbo_hdr),
>+			       tcp_hdrlen(skb));
>+			/* Leave ipv6 payload_len set to 0, as LSO v2 specs request. */
>+		} else if (skb_vlan_tag_present(skb)) {
>+			mlx5e_insert_vlan(start, skb, ihs);
>+			ihs += VLAN_HLEN;
> 			stats->added_vlan_packets++;
> 		} else {
>-			eseg->inline_hdr.sz |= cpu_to_be16(attr->ihs);
>-			memcpy(eseg->inline_hdr.start, skb->data, attr->ihs);
>+			memcpy(start, skb->data, ihs);
> 		}
>+		eseg->inline_hdr.sz |= cpu_to_be16(ihs);
> 		dseg += wqe_attr->ds_cnt_inl;
> 	} else if (skb_vlan_tag_present(skb)) {
> 		eseg->insert.type = cpu_to_be16(MLX5_ETH_WQE_INSERT_VLAN);
>@@ -398,7 +433,7 @@ mlx5e_sq_xmit_wqe(struct mlx5e_txqsq *sq, struct sk_buff *skb,
> 	}
>
> 	dseg += wqe_attr->ds_cnt_ids;
>-	num_dma = mlx5e_txwqe_build_dsegs(sq, skb, skb->data + attr->ihs,
>+	num_dma = mlx5e_txwqe_build_dsegs(sq, skb, skb->data + attr->ihs + attr->hopbyhop,
> 					  attr->headlen, dseg);
> 	if (unlikely(num_dma < 0))
> 		goto err_drop;
>@@ -918,12 +953,29 @@ void mlx5i_sq_xmit(struct mlx5e_txqsq *sq, struct sk_buff *skb,
> 	eseg->mss = attr.mss;
>
> 	if (attr.ihs) {
>-		memcpy(eseg->inline_hdr.start, skb->data, attr.ihs);
>+		if (unlikely(attr.hopbyhop)) {
>+			struct ipv6hdr *h6;
>+
>+			/* remove the HBH header.
>+			 * Layout: [Ethernet header][IPv6 header][HBH][TCP header]
>+			 */
>+			memcpy(eseg->inline_hdr.start, skb->data, ETH_HLEN + sizeof(*h6));
>+			h6 = (struct ipv6hdr *)((char *)eseg->inline_hdr.start + ETH_HLEN);
>+			h6->nexthdr = IPPROTO_TCP;
>+			/* Copy the TCP header after the IPv6 one */
>+			memcpy(h6 + 1,
>+			       skb->data + ETH_HLEN + sizeof(*h6) +
>+					sizeof(struct hop_jumbo_hdr),
>+			       tcp_hdrlen(skb));
>+			/* Leave ipv6 payload_len set to 0, as LSO v2 specs request. */
>+		} else {
>+			memcpy(eseg->inline_hdr.start, skb->data, attr.ihs);
>+		}
> 		eseg->inline_hdr.sz = cpu_to_be16(attr.ihs);
> 		dseg += wqe_attr.ds_cnt_inl;
> 	}
>
>-	num_dma = mlx5e_txwqe_build_dsegs(sq, skb, skb->data + attr.ihs,
>+	num_dma = mlx5e_txwqe_build_dsegs(sq, skb, skb->data + attr.ihs + attr.hopbyhop,
> 					  attr.headlen, dseg);
> 	if (unlikely(num_dma < 0))
> 		goto err_drop;
>-- 
>2.36.0.512.ge40c2bad7a-goog
>

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