Re: [PATCH net-next] net: mana: Linearize SKB if TX SGEs exceeds hardware limit
From: Simon Horman <horms@kernel.org>
Date: 2025-10-04 09:38:12
Also in:
linux-hyperv, linux-rdma, lkml
On Fri, Oct 03, 2025 at 08:47:24AM -0700, Aditya Garg wrote:
quoted hunk ↗ jump to hunk
The MANA hardware supports a maximum of 30 scatter-gather entries (SGEs) per TX WQE. In rare configurations where MAX_SKB_FRAGS + 2 exceeds this limit, the driver drops the skb. Add a check in mana_start_xmit() to detect such cases and linearize the SKB before transmission. Return NETDEV_TX_BUSY only for -ENOSPC from mana_gd_post_work_request(), send other errors to free_sgl_ptr to free resources and record the tx drop. Signed-off-by: Aditya Garg <redacted> Reviewed-by: Dipayaan Roy <redacted> --- drivers/net/ethernet/microsoft/mana/mana_en.c | 26 +++++++++++++++---- include/net/mana/gdma.h | 8 +++++- include/net/mana/mana.h | 1 + 3 files changed, 29 insertions(+), 6 deletions(-)diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c index f4fc86f20213..22605753ca84 100644 --- a/drivers/net/ethernet/microsoft/mana/mana_en.c +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c@@ -20,6 +20,7 @@ #include <net/mana/mana.h> #include <net/mana/mana_auxiliary.h> +#include <linux/skbuff.h> static DEFINE_IDA(mana_adev_ida);@@ -289,6 +290,19 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev) cq = &apc->tx_qp[txq_idx].tx_cq; tx_stats = &txq->stats; + BUILD_BUG_ON(MAX_TX_WQE_SGL_ENTRIES != MANA_MAX_TX_WQE_SGL_ENTRIES); + #if (MAX_SKB_FRAGS + 2 > MANA_MAX_TX_WQE_SGL_ENTRIES)
Hi Aditya, I see that Eric has made a more substantial review of this patch, so please follow his advice. But I wanted to add something to keep in mind for the future: I if the #if / #else used here can be replaced by a simple if() statement, then that would be preferable. The advantage being that it improves compile coverage. And, as these are all constants, I would expect the compiler to optimise away any unused code. N.B: I did not check, so please consider this more of a general statement
+ if (skb_shinfo(skb)->nr_frags + 2 > MANA_MAX_TX_WQE_SGL_ENTRIES) {
+ netdev_info_once(ndev,
+ "nr_frags %d exceeds max supported sge limit. Attempting skb_linearize\n",
+ skb_shinfo(skb)->nr_frags);
+ if (skb_linearize(skb)) {
+ netdev_warn_once(ndev, "Failed to linearize skb\n");
+ goto tx_drop_count;
+ }
+ }
+ #endif
+
pkg.tx_oob.s_oob.vcq_num = cq->gdma_id;
pkg.tx_oob.s_oob.vsq_frame = txq->vsq_frame;
...