netdev - [PATCH net-next 4/9] net: enetc: clean the TX software BD on the TX confirmation path

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Date:   Wed, 31 Mar 2021 23:08:52 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     Alexander Duyck <alexander.duyck@...il.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Alex Marginean <alexandru.marginean@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: [PATCH net-next 4/9] net: enetc: clean the TX software BD on the TX confirmation path

From: Vladimir Oltean <vladimir.oltean@....com>

With the future introduction of some new fields into enetc_tx_swbd such
as is_xdp_tx, is_xdp_redirect etc, we need not only to set these bits
to true from the XDP_TX/XDP_REDIRECT code path, but also to false from
the old code paths.

This is because TX software buffer descriptors are kept in a ring that
is shadow of the hardware TX ring, so these structures keep getting
reused, and there is always the possibility that when a software BD is
reused (after we ran a full circle through the TX ring), the old user of
the tx_swbd had set is_xdp_tx = true, and now we are sending a regular
skb, which would need to set is_xdp_tx = false.

To be minimally invasive to the old code paths, let's just scrub the
software TX BD in the TX confirmation path (enetc_clean_tx_ring), once
we know that nobody uses this software TX BD (tx_ring->next_to_clean
hasn't yet been updated, and the TX paths check enetc_bd_unused which
tells them if there's any more space in the TX ring for a new enqueue).

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/net/ethernet/freescale/enetc/enetc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index 37d2d142a744..ade05518b496 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -344,6 +344,10 @@ static bool enetc_clean_tx_ring(struct enetc_bdr *tx_ring, int napi_budget)
 		}

 		tx_byte_cnt += tx_swbd->len;
+		/* Scrub the swbd here so we don't have to do that
+		 * when we reuse it during xmit
+		 */
+		memset(tx_swbd, 0, sizeof(*tx_swbd));

 		bds_to_clean--;
 		tx_swbd++;
-- 
2.25.1