linux-kernel - Re: [PATCH v2 net] net: enetc: Do not configure preemptible TCs if SIs do not support

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Message-ID: <20241106143954.3avqol5m7j6i7hrt@skbuf>
Date: Wed, 6 Nov 2024 16:49:46 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Wei Fang <wei.fang@....com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, andrew+netdev@...n.ch, claudiu.manoil@....com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	imx@...ts.linux.dev
Subject: Re: [PATCH v2 net] net: enetc: Do not configure preemptible TCs if
 SIs do not support

On Mon, Nov 04, 2024 at 01:43:09PM +0800, Wei Fang wrote:
> Both ENETC PF and VF drivers share enetc_setup_tc_mqprio() to configure
> MQPRIO. And enetc_setup_tc_mqprio() calls enetc_change_preemptible_tcs()
> to configure preemptible TCs. However, only PF is able to configure
> preemptible TCs. Because only PF has related registers, while VF does not
> have these registers. So for VF, its hw->port pointer is NULL. Therefore,
> VF will access an invalid pointer when accessing a non-existent register,
> which will cause a call trace issue. The simplified log is as follows.
> 
> root@...028ardb:~# tc qdisc add dev eno0vf0 parent root handle 100: \
> mqprio num_tc 4 map 0 0 1 1 2 2 3 3 queues 1@0 1@1 1@2 1@3 hw 1
> [  187.290775] Unable to handle kernel paging request at virtual address 0000000000001f00
> [  187.424831] pc : enetc_mm_commit_preemptible_tcs+0x1c4/0x400
> [  187.430518] lr : enetc_mm_commit_preemptible_tcs+0x30c/0x400
> [  187.511140] Call trace:
> [  187.513588]  enetc_mm_commit_preemptible_tcs+0x1c4/0x400
> [  187.518918]  enetc_setup_tc_mqprio+0x180/0x214
> [  187.523374]  enetc_vf_setup_tc+0x1c/0x30
> [  187.527306]  mqprio_enable_offload+0x144/0x178
> [  187.531766]  mqprio_init+0x3ec/0x668
> [  187.535351]  qdisc_create+0x15c/0x488
> [  187.539023]  tc_modify_qdisc+0x398/0x73c
> [  187.542958]  rtnetlink_rcv_msg+0x128/0x378
> [  187.547064]  netlink_rcv_skb+0x60/0x130
> [  187.550910]  rtnetlink_rcv+0x18/0x24
> [  187.554492]  netlink_unicast+0x300/0x36c
> [  187.558425]  netlink_sendmsg+0x1a8/0x420
> [  187.606759] ---[ end trace 0000000000000000 ]---
> 
> In addition, some PFs also do not support configuring preemptible TCs,
> such as eno1 and eno3 on LS1028A. It won't crash like it does for VFs,
> but we should prevent these PFs from accessing these unimplemented
> registers.
> 
> Fixes: 827145392a4a ("net: enetc: only commit preemptible TCs to hardware when MM TX is active")
> Signed-off-by: Wei Fang <wei.fang@....com>
> Suggested-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
> v1 Link: https://lore.kernel.org/imx/20241030082117.1172634-1-wei.fang@nxp.com/
> v2 changes:
> 1. Change the title and refine the commit message
> 2. Only set ENETC_SI_F_QBU bit for PFs which support Qbu
> 3. Prevent all SIs which not support Qbu from configuring preemptible
> TCs
> ---
>  drivers/net/ethernet/freescale/enetc/enetc.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
> index c09370eab319..59d4ca52dc21 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> @@ -28,6 +28,9 @@ EXPORT_SYMBOL_GPL(enetc_port_mac_wr);
>  static void enetc_change_preemptible_tcs(struct enetc_ndev_priv *priv,
>  					 u8 preemptible_tcs)
>  {
> +	if (!(priv->si->hw_features & ENETC_SI_F_QBU))
> +		return;
> +
>  	priv->preemptible_tcs = preemptible_tcs;
>  	enetc_mm_commit_preemptible_tcs(priv);
>  }
> @@ -1752,7 +1755,12 @@ void enetc_get_si_caps(struct enetc_si *si)
>  	if (val & ENETC_SIPCAPR0_QBV)
>  		si->hw_features |= ENETC_SI_F_QBV;
>  
> -	if (val & ENETC_SIPCAPR0_QBU)
> +	/* Although the SIPCAPR0 of VF indicates that VF supports Qbu,
> +	 * only PF can access the related registers to configure Qbu.
> +	 * Therefore, ENETC_SI_F_QBU is set only for PFs which support
> +	 * this feature.
> +	 */
> +	if (val & ENETC_SIPCAPR0_QBU && enetc_si_is_pf(si))
>  		si->hw_features |= ENETC_SI_F_QBU;
>  
>  	if (val & ENETC_SIPCAPR0_PSFP)
> -- 
> 2.34.1
>

As per internal discussions, the correct fix would be to read these
hw_features from the ENETC_PCAPR0 register rather than ENETC_SIPCAPR0,
and have this code exclusively in the PF driver.

I'm expecting a new change which moves the capability detection which is
similar to what I have attached here, and then your patch will only contain
the snippet from enetc_change_preemptible_tcs() which you've already posted.

pw-bot: changes-requested

View attachment "0001-net-enetc-read-TSN-capabilities-from-port-register-n.patch" of type "text/x-diff" (5485 bytes)