FAILED: patch "[PATCH] net: mvpp2: fix XDP rx queues registering" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a50e659b2a1be14784e80f8492aab177e67c53a2 Mon Sep 17 00:00:00 2001
From: Louis Amas <[email protected]>
Date: Tue, 7 Dec 2021 15:34:22 +0100
Subject: [PATCH] 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.

index 6480696c979b..6da8a595026b 100644
@@ -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;
 

Hello Greg,

I guess that some context changed since we tested the backport. We'll send it back as soon as possible (Louis is working on this right now).

Best regards,

-- Emmanuel Deloget