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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: edumazet@google.com, horms@kernel.org, linux-kernel@vger.kernel.org, Joe Damato Subject: [PATCH net-next v2 2/2] bnxt_en: Pad short SW USO segments to BNXT_MIN_PKT_SIZE Date: Fri, 9 Oct 2026 14:54:24 -0700 Message-ID: <20261009215426.2377946-3-joe@dama.to> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261009215426.2377946-1-joe@dama.to> References: <20261009215426.2377946-1-joe@dama.to> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Each SW USO segment is hdr_len + seg_payload bytes. With IPv4, hdr_len is 42 bytes, so a segment carrying less than 10 bytes of UDP payload is sent shorter than BNXT_MIN_PKT_SIZE. This happens with a short last segment (e.g. gso_size 1400 and 1405 bytes of payload) or with a gso_size below 10 bytes. Fix the short last segment in bnxt_sw_udp_gso_xmit(): zero the pad bytes after the header in the segment's inline header slot and add a pad BD pointing at them after the payload BDs. Only the last segment can need padding, and its pad BD fits within the existing bound in bds_needed and BNXT_SW_USO_MAX_DESCS, since payload BDs are at most num_segs + nr_frags. If gso_size itself is too small, every segment would need a pad BD, exceeding the descriptor bound. This case is unlikely, so bnxt_features_check() clears GSO features for these skbs and the stack segments them instead; bnxt_start_xmit() then pads each segment. Reviewed-by: Michael Chan Signed-off-by: Joe Damato --- drivers/net/ethernet/broadcom/bnxt/bnxt.c | 12 ++++++++ drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c | 28 +++++++++++++++++-- drivers/net/ethernet/broadcom/bnxt/bnxt_gso.h | 15 ++++++++++ 3 files changed, 53 insertions(+), 2 deletions(-) diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c index c1d3fcc7ae84..0682060b048c 100644 --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c @@ -14268,6 +14268,18 @@ static netdev_features_t bnxt_features_check(struct sk_buff *skb, u8 *l4_proto; features = vlan_features_check(skb, features); + + /* SW USO pads at most the last segment; let the stack segment skbs + * where every segment would be shorter than BNXT_MIN_PKT_SIZE. + */ + if (skb_is_gso(skb) && + (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) && + !(bp->flags & BNXT_FLAG_UDP_GSO_CAP) && + bnxt_sw_gso_pad_len(skb_transport_offset(skb) + + sizeof(struct udphdr), + skb_shinfo(skb)->gso_size)) + features &= ~NETIF_F_GSO_MASK; + switch (vlan_get_protocol(skb)) { case htons(ETH_P_IP): if (!skb->encapsulation) diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c index ef04c9d08066..80d5c4f963a9 100644 --- a/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c @@ -82,11 +82,19 @@ int bnxt_sw_udp_gso_xmit(struct bnxt *bp, struct bnxt_tx_ring_info *txr, if (unlikely(num_segs <= 1)) goto drop; + /* bnxt_features_check() makes the stack segment these, but paths + * that skip validate_xmit_skb() (e.g. generic XDP_TX of a GRO'd + * skb) can still get here. Padding every segment would need more + * BDs than bds_needed reserves below, so drop instead. + */ + if (unlikely(bnxt_sw_gso_pad_len(hdr_len, mss))) + goto drop; + /* Upper bound on the number of descriptors needed. * * Each segment uses 1 long BD + 1 ext BD + payload BDs, which is * at most num_segs + nr_frags (each frag boundary crossing adds at - * most 1 extra BD). + * most 1 extra BD). The last segment may need 1 pad BD. */ bds_needed = 3 * num_segs + skb_shinfo(skb)->nr_frags + 1; @@ -133,12 +141,14 @@ int bnxt_sw_udp_gso_xmit(struct bnxt *bp, struct bnxt_tx_ring_info *txr, dma_addr_t dma_addr; struct tx_bd *txbd; struct udphdr *uh; + unsigned int pad; void *this_hdr; int bd_count; bool last; u32 flags; last = (i == num_segs - 1); + pad = bnxt_sw_gso_pad_len(hdr_len, seg_payload); offset = slot * TSO_HEADER_SIZE; this_hdr = txr->tx_inline_buf + offset; this_hdr_dma = txr->tx_inline_dma + offset; @@ -156,10 +166,18 @@ int bnxt_sw_udp_gso_xmit(struct bnxt *bp, struct bnxt_tx_ring_info *txr, iph->check = 0; } + /* Pad bytes follow the header in the inline slot. Zero them + * so stale header bytes from an earlier packet are not sent. + */ + if (pad) + memset(this_hdr + hdr_len, 0, pad); + dma_sync_single_for_device(&pdev->dev, this_hdr_dma, - hdr_len, DMA_TO_DEVICE); + hdr_len + pad, DMA_TO_DEVICE); bd_count = tso_dma_map_count(&map, seg_payload); + if (pad) + bd_count++; tx_buf = &txr->tx_buf_ring[RING_TX(bp, prod)]; txbd = &txr->tx_desc_ring[TX_RING(bp, prod)][TX_IDX(prod)]; @@ -222,6 +240,12 @@ int bnxt_sw_udp_gso_xmit(struct bnxt *bp, struct bnxt_tx_ring_info *txr, seg_payload -= chunk_len; } + if (pad) { + prod = NEXT_TX(prod); + txbd = bnxt_sw_gso_data_bd(bp, txr, prod, + this_hdr_dma + hdr_len, pad); + } + txbd->tx_bd_len_flags_type |= cpu_to_le32(TX_BD_FLAGS_PACKET_END); diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.h b/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.h index 77d9af97cc22..5916ee08c0e6 100644 --- a/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.h +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.h @@ -19,10 +19,25 @@ * Each segment: 1 long BD + 1 ext BD + payload BDs. * Total payload BDs across all segs <= num_segs + nr_frags (each frag * boundary crossing adds at most 1 extra BD). + * The last segment may need 1 pad BD (see bnxt_sw_gso_pad_len()). * So: 3 * max_segs + MAX_SKB_FRAGS + 1 = 3 * 64 + 17 + 1 = 210. */ #define BNXT_SW_USO_MAX_DESCS (3 * BNXT_SW_USO_MAX_SEGS + MAX_SKB_FRAGS + 1) +/* Bytes of padding needed to bring a segment carrying @seg_payload bytes + * up to BNXT_MIN_PKT_SIZE, or 0 if no padding is needed. + */ +static inline unsigned int bnxt_sw_gso_pad_len(unsigned int hdr_len, + unsigned int seg_payload) +{ + unsigned int len = hdr_len + seg_payload; + + if (len < BNXT_MIN_PKT_SIZE) + return BNXT_MIN_PKT_SIZE - len; + else + return 0; +} + static inline u16 bnxt_inline_avail(struct bnxt_tx_ring_info *txr) { return BNXT_SW_USO_MAX_SEGS - -- 2.53.0-Meta