qede: execute xdp_do_flush() before napi_complete_done()

[ Upstream commit 2ccce20d51faa0178086163ccb6c84a099a87ab4 ]

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 followed 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@intel.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.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/
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/net/ethernet/qlogic/qede/qede_fp.c b/drivers/net/ethernet/qlogic/qede/qede_fp.c
index 5b1885c0a8bd8f2bb683d8d3bd0fbe471d663165..a632de208a7dc6a91e78505134da5c9c93660eb8 100644 (file)
--- a/drivers/net/ethernet/qlogic/qede/qede_fp.c
+++ b/drivers/net/ethernet/qlogic/qede/qede_fp.c
@@ -1456,6 +1456,10 @@ 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)) {
@@ -1475,9 +1479,6 @@ 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;
 }