netdev - Re: [PATCH net-next v4 11/11] net: dsa: realtek: rtl8365mb: multiple cpu ports, non cpu extint

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Message-ID: <20220124190845.md3m2wzu7jx4xtpr@skbuf>
Date:   Mon, 24 Jan 2022 21:08:45 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Luiz Angelo Daros de Luca <luizluca@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Frank Wunderlich <frank-w@...lic-files.de>,
        Alvin Šipraga <ALSI@...g-olufsen.dk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "vivien.didelot@...il.com" <vivien.didelot@...il.com>,
        "arinc.unal@...nc9.com" <arinc.unal@...nc9.com>
Subject: Re: [PATCH net-next v4 11/11] net: dsa: realtek: rtl8365mb: multiple
 cpu ports, non cpu extint

On Mon, Jan 24, 2022 at 10:20:51AM -0800, Jakub Kicinski wrote:
> On Mon, 24 Jan 2022 09:35:56 -0800 Jakub Kicinski wrote:
> > Sorry I used "geometry" loosely.
> >
> > What I meant is simply that if the driver uses NETIF_F_IP*_CSUM
> > it should parse the packet before it hands it off to the HW.
> >
> > There is infinity of protocols users can come up with, while the device
> > parser is very much finite, so it's only practical to check compliance
> > with the HW parser in the driver. The reverse approach of adding
> > per-protocol caps is a dead end IMO. And we should not bloat the stack
> > when NETIF_F_HW_CSUM exists and the memo that parsing packets on Tx is
> > bad b/c of protocol ossification went out a decade ago.
>
> > It's not about DSA. The driver should not check
> >
> > if (dsa())
> > 	blah;
> >
> > it should check
> >
> > if (!(eth [-> vlan] -> ip -> tcp/udp))
> > 	csum_help();
>
> Admittedly on a quick look thru the drivers which already do this
> I only see L3, L4 and GRE/UDP encap checks. Nothing validates L2.

So before we declare that any given Ethernet driver is buggy for declaring
NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM and not checking that skb->csum_start
points where it expects it to (taking into consideration potential VLAN
headers, IPv6 extension headers), is there any driver that _does_
perform these checks correctly, that could be used as an example?