[PATCH 5.16 0438/1017] i40e: dont reserve excessive XDP_PACKET_HEADROOM on XSK Rx to skb

From: Greg Kroah-Hartman
Date: Tue Apr 05 2022 - 08:04:32 EST

From: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>

[ Upstream commit bc97f9c6f988b31b728eb47a94ca825401dbeffe ]

{__,}napi_alloc_skb() allocates and reserves additional NET_SKB_PAD
+ NET_IP_ALIGN for any skb.
OTOH, i40e_construct_skb_zc() currently allocates and reserves
additional `xdp->data - xdp->data_hard_start`, which is
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 to __napi_alloc_skb() and
don't reserve anything. This will give enough headroom for stack

Fixes: 0a714186d3c0 ("i40e: add AF_XDP zero-copy Rx support")
Signed-off-by: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@xxxxxxxxxxxxxxx>
Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Tested-by: Kiran Bhandare <kiranx.bhandare@xxxxxxxxx>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
drivers/net/ethernet/intel/i40e/i40e_xsk.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
index ea06e957393e..dff7c7fcc329 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
@@ -246,13 +246,11 @@ static struct sk_buff *i40e_construct_skb_zc(struct i40e_ring *rx_ring,
struct sk_buff *skb;

/* allocate a skb to store the frags */
- skb = __napi_alloc_skb(&rx_ring->q_vector->napi,
- xdp->data_end - xdp->data_hard_start,
+ skb = __napi_alloc_skb(&rx_ring->q_vector->napi, datasize,
if (unlikely(!skb))
goto out;

- skb_reserve(skb, xdp->data - xdp->data_hard_start);
memcpy(__skb_put(skb, datasize), xdp->data, datasize);
if (metasize)
skb_metadata_set(skb, metasize);