On 03-10-2025 21:45, Eric Dumazet wrote:
On Fri, Oct 3, 2025 at 8:47 AM Aditya Garg
<[email protected]> wrote:
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 <[email protected]>
Reviewed-by: Dipayaan Roy <[email protected]>
---
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)
+ 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)) {
This will fail in many cases.
This sort of check is better done in ndo_features_check()
Most probably this would occur for GSO packets, so can ask a software
segmentation
to avoid this big and risky kmalloc() by all means.
Look at idpf_features_check() which has something similar.
Hi Eric,
Thank you for your review. I understand your concerns regarding the use
of skb_linearize() in the xmit path, as it can fail under memory
pressure and introduces additional overhead in the transmit path. Based
on your input, I will work on a v2 that will move the SGE limit check to
the ndo_features_check() path and for GSO skbs exceding the hw limit
will disable the NETIF_F_GSO_MASK to enforce software segmentation in
kernel before the call to xmit.
Also for non GSO skb exceeding the SGE hw limit should we go for using
skb_linearize only then or would you suggest some other approach here?
Regards,
Aditya
