netdev - [PATCH net 1/5] qede: execute xdp_do_flush() before napi_complete

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Message-Id: <20230117092533.5804-2-magnus.karlsson@gmail.com>
Date:   Tue, 17 Jan 2023 10:25:29 +0100
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     magnus.karlsson@...el.com, bjorn@...nel.org, ast@...nel.org,
        daniel@...earbox.net, netdev@...r.kernel.org,
        jonathan.lemon@...il.com, maciej.fijalkowski@...el.com,
        kuba@...nel.org, toke@...hat.com, pabeni@...hat.com,
        davem@...emloft.net, aelior@...vell.com, manishc@...vell.com,
        horatiu.vultur@...rochip.com, UNGLinuxDriver@...rochip.com,
        mst@...hat.com, jasowang@...hat.com, ioana.ciornei@....com,
        madalin.bucur@....com
Cc:     bpf@...r.kernel.org
Subject: [PATCH net 1/5] qede: execute xdp_do_flush() before napi_complete_done()

From: Magnus Karlsson <magnus.karlsson@...el.com>

Make sure that xdp_do_flush() is always executed before
napi_complete_done(). This is important for two reasons. First, a
redirect to an XSKMAP assumes that a call to xdp_do_redirect() from
napi context X on CPU Y will be follwed by a xdp_do_flush() from the
same napi context and CPU. This is not guaranteed if the
napi_complete_done() is executed before xdp_do_flush(), as it tells
the napi logic that it is fine to schedule napi context X on another
CPU. Details from a production system triggering this bug using the
veth driver can be found following the first link below.

The second reason is that the XDP_REDIRECT logic in itself relies on
being inside a single NAPI instance through to the xdp_do_flush() call
for RCU protection of all in-kernel data structures. Details can be
found in the second link below.

Fixes: d1b25b79e162b ("qede: add .ndo_xdp_xmit() and XDP_REDIRECT support")
Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
Link: https://lore.kernel.org/r/20221220185903.1105011-1-sbohrer@cloudflare.com
Link: https://lore.kernel.org/all/20210624160609.292325-1-toke@redhat.com/
---
 drivers/net/ethernet/qlogic/qede/qede_fp.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/qlogic/qede/qede_fp.c b/drivers/net/ethernet/qlogic/qede/qede_fp.c
index 7c2af482192d..cb1746bc0e0c 100644
--- a/drivers/net/ethernet/qlogic/qede/qede_fp.c
+++ b/drivers/net/ethernet/qlogic/qede/qede_fp.c
@@ -1438,6 +1438,10 @@ int qede_poll(struct napi_struct *napi, int budget)
 	rx_work_done = (likely(fp->type & QEDE_FASTPATH_RX) &&
 			qede_has_rx_work(fp->rxq)) ?
 			qede_rx_int(fp, budget) : 0;
+
+	if (fp->xdp_xmit & QEDE_XDP_REDIRECT)
+		xdp_do_flush();
+
 	/* Handle case where we are called by netpoll with a budget of 0 */
 	if (rx_work_done < budget || !budget) {
 		if (!qede_poll_is_more_work(fp)) {
@@ -1457,9 +1461,6 @@ int qede_poll(struct napi_struct *napi, int budget)
 		qede_update_tx_producer(fp->xdp_tx);
 	}
 
-	if (fp->xdp_xmit & QEDE_XDP_REDIRECT)
-		xdp_do_flush_map();
-
 	return rx_work_done;
 }
 
-- 
2.34.1