linux-kernel - [PATCH v4 net 1/1] net: mvpp2: fix XDP rx queues registering

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Message-Id: <20211207142017.900582-1-louis.amas@eho.link>
Date:   Tue,  7 Dec 2021 15:20:16 +0100
From:   Louis Amas <louis.amas@....link>
To:     Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        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>,
        Matteo Croce <mcroce@...rosoft.com>
Cc:     Louis Amas <louis.amas@....link>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH v4 net 1/1] net: mvpp2: fix XDP rx queues registering

The registration of XDP queue information is incorrect because the
RX queue id we use is invalid. When port->id == 0 it appears to works
as expected yet it's no longer the case when port->id != 0.

The problem arised while using a recent kernel version on the
MACCHIATOBin. This board has several ports:
 * eth0 and eth1 are 10Gbps interfaces ; both ports has port->id == 0;
 * eth2 is a 1Gbps interface with port->id != 0.

Code from xdp-tutorial (more specifically advanced03-AF_XDP) was used
to test packet capture and injection on all these interfaces. The XDP
kernel was simplified to:

	SEC("xdp_sock")
	int xdp_sock_prog(struct xdp_md *ctx)
	{
		int index = ctx->rx_queue_index;

		/* A set entry here means that the correspnding queue_id
		* has an active AF_XDP socket bound to it. */
		if (bpf_map_lookup_elem(&xsks_map, &index))
			return bpf_redirect_map(&xsks_map, index, 0);

		return XDP_PASS;
	}

Starting the program using:

	./af_xdp_user -d DEV

Gives the following result:

 * eth0 : ok
 * eth1 : ok
 * eth2 : no capture, no injection

Investigating the issue shows that XDP rx queues for eth2 are wrong:
XDP expects their id to be in the range [0..3] but we found them to be
in the range [32..35].

Trying to force rx queue ids using:

	./af_xdp_user -d eth2 -Q 32

fails as expected (we shall not have more than 4 queues).

When we register the XDP rx queue information (using
xdp_rxq_info_reg() in function mvpp2_rxq_init()) we tell it to use
rxq->id as the queue id. This value is computed as:

	rxq->id = port->id * max_rxq_count + queue_id

where max_rxq_count depends on the device version. In the MACCHIATOBin
case, this value is 32, meaning that rx queues on eth2 are numbered
from 32 to 35 - there are four of them.

Clearly, this is not the per-port queue id that XDP is expecting:
it wants a value in the range [0..3]. It shall directly use queue_id
which is stored in rxq->logic_rxq -- so let's use that value instead.

rxq->id is left untouched ; its value is indeed valid but it should
not be used in this context.

This is consistent with the remaining part of the code in
mvpp2_rxq_init().

With this change, packet capture is working as expected on all the
MACCHIATOBin ports.

Fixes: b27db2274ba8 ("mvpp2: use page_pool allocator")
Signed-off-by: Louis Amas <louis.amas@....link>
---

Patch history

v1 : original submission [1]
v2 : commit message rework (no change in the patch) [2]
v3 : commit message rework (no change in the patch) + added Acked-by [3]
v4 : (this version) fix mail corruption by malevolent SMTP + rebase on net/master

[1] https://lore.kernel.org/bpf/20211109103101.92382-1-louis.amas@eho.link/
[2] https://lore.kernel.org/bpf/20211110144104.241589-1-louis.amas@eho.link/
[3] https://lore.kernel.org/bpf/20211206172220.602024-1-louis.amas@eho.link/

 drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
index 6480696c979b..6da8a595026b 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
@@ -2960,11 +2960,11 @@ static int mvpp2_rxq_init(struct mvpp2_port *port,
 	mvpp2_rxq_status_update(port, rxq->id, 0, rxq->size);

 	if (priv->percpu_pools) {
-		err = xdp_rxq_info_reg(&rxq->xdp_rxq_short, port->dev, rxq->id, 0);
+		err = xdp_rxq_info_reg(&rxq->xdp_rxq_short, port->dev, rxq->logic_rxq, 0);
 		if (err < 0)
 			goto err_free_dma;

-		err = xdp_rxq_info_reg(&rxq->xdp_rxq_long, port->dev, rxq->id, 0);
+		err = xdp_rxq_info_reg(&rxq->xdp_rxq_long, port->dev, rxq->logic_rxq, 0);
 		if (err < 0)
 			goto err_unregister_rxq_short;

-- 
2.25.1