[PATCH 5.17 0483/1126] igc: dont reserve excessive XDP_PACKET_HEADROOM on XSK Rx to skb

From: Greg Kroah-Hartman
Date: Tue Apr 05 2022 - 04:56:02 EST

From: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>

[ Upstream commit f9e61d365bafdee40fe2586fc6be490c3e824dad ]

{__,}napi_alloc_skb() allocates and reserves additional NET_SKB_PAD
+ NET_IP_ALIGN for any skb.
OTOH, igc_construct_skb_zc() currently allocates and reserves
additional `xdp->data_meta - xdp->data_hard_start`, which is about
There's no need for that at all as the frame is post-XDP and will
go only to the networking stack core.
Pass the size of the actual data only (+ meta) to
__napi_alloc_skb() and don't reserve anything. This will give
enough headroom for stack processing.
Also, net_prefetch() xdp->data_meta and align the copy size to
speed-up memcpy() a little and better match igc_construct_skb().

Fixes: fc9df2a0b520 ("igc: Enable RX via AF_XDP zero-copy")
Signed-off-by: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@xxxxxxxxxxxxxxx>
Tested-by: Nechama Kraus <nechamax.kraus@xxxxxxxxxxxxxxx>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
drivers/net/ethernet/intel/igc/igc_main.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 2f17f36e94fd..629e4a644a9d 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -2446,19 +2446,20 @@ static int igc_clean_rx_irq(struct igc_q_vector *q_vector, const int budget)
static struct sk_buff *igc_construct_skb_zc(struct igc_ring *ring,
struct xdp_buff *xdp)
+ unsigned int totalsize = xdp->data_end - xdp->data_meta;
unsigned int metasize = xdp->data - xdp->data_meta;
- unsigned int datasize = xdp->data_end - xdp->data;
- unsigned int totalsize = metasize + datasize;
struct sk_buff *skb;

- skb = __napi_alloc_skb(&ring->q_vector->napi,
- xdp->data_end - xdp->data_hard_start,
+ net_prefetch(xdp->data_meta);
+ skb = __napi_alloc_skb(&ring->q_vector->napi, totalsize,
if (unlikely(!skb))
return NULL;

- skb_reserve(skb, xdp->data_meta - xdp->data_hard_start);
- memcpy(__skb_put(skb, totalsize), xdp->data_meta, totalsize);
+ memcpy(__skb_put(skb, totalsize), xdp->data_meta,
+ ALIGN(totalsize, sizeof(long)));
if (metasize) {
skb_metadata_set(skb, metasize);
__skb_pull(skb, metasize);