netdev - Re: [PATCH net] r8169: work around RTL8125 UDP hw bug

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Message-ID: <CAF=yD-Jw6MqY+hnzFH75E4+3z5jo8dnO5G+KXpTd_vetZ6Gxwg@mail.gmail.com>
Date:   Wed, 27 Jan 2021 13:07:46 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        xplo.bn@...il.com
Subject: Re: [PATCH net] r8169: work around RTL8125 UDP hw bug

On Tue, Jan 26, 2021 at 2:40 PM Heiner Kallweit <hkallweit1@...il.com> wrote:
>
> It was reported that on RTL8125 network breaks under heavy UDP load,
> e.g. torrent traffic ([0], from comment 27). Realtek confirmed a hw bug
> and provided me with a test version of the r8125 driver including a
> workaround. Tests confirmed that the workaround fixes the issue.
> I modified the original version of the workaround to meet mainline
> code style.
>
> [0] https://bugzilla.kernel.org/show_bug.cgi?id=209839
>
> Fixes: f1bce4ad2f1c ("r8169: add support for RTL8125")
> Tested-by: xplo <xplo.bn@...il.com>
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
>  drivers/net/ethernet/realtek/r8169_main.c | 64 ++++++++++++++++++++---
>  1 file changed, 58 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
> index fb67d8f79..90052033b 100644
> --- a/drivers/net/ethernet/realtek/r8169_main.c
> +++ b/drivers/net/ethernet/realtek/r8169_main.c
> @@ -28,6 +28,7 @@
>  #include <linux/bitfield.h>
>  #include <linux/prefetch.h>
>  #include <linux/ipv6.h>
> +#include <linux/ptp_classify.h>
>  #include <asm/unaligned.h>
>  #include <net/ip6_checksum.h>
>
> @@ -4007,17 +4008,64 @@ static int rtl8169_xmit_frags(struct rtl8169_private *tp, struct sk_buff *skb,
>         return -EIO;
>  }
>
> -static bool rtl_test_hw_pad_bug(struct rtl8169_private *tp)
> +static bool rtl_skb_is_udp(struct sk_buff *skb)
>  {
> +       switch (vlan_get_protocol(skb)) {
> +       case htons(ETH_P_IP):
> +               return ip_hdr(skb)->protocol == IPPROTO_UDP;
> +       case htons(ETH_P_IPV6):
> +               return ipv6_hdr(skb)->nexthdr == IPPROTO_UDP;

This trusts that an skb with given skb->protocol is well behaved. With
packet sockets/tun/virtio, that may be false.

> +       default:
> +               return false;
> +       }
> +}
> +
> +#define RTL_MIN_PATCH_LEN      47
> +#define PTP_GEN_PORT           320

Why the two PTP ports? The report is not PTP specific. Also, what does
patch mean in this context?

> +
> +/* see rtl8125_get_patch_pad_len() in r8125 vendor driver */
> +static unsigned int rtl8125_quirk_udp_padto(struct rtl8169_private *tp,
> +                                           struct sk_buff *skb)
> +{
> +       unsigned int padto = 0, len = skb->len;
> +
> +       if (rtl_is_8125(tp) && len < 175 && rtl_skb_is_udp(skb) &&
> +           skb_transport_header_was_set(skb)) {

What is 175 here?

> +               unsigned int trans_data_len = skb_tail_pointer(skb) -
> +                                             skb_transport_header(skb);
> +
> +               if (trans_data_len > 3 && trans_data_len < RTL_MIN_PATCH_LEN) {

And 3 here, instead of sizeof(struct udphdr)

> +                       u16 dest = ntohs(udp_hdr(skb)->dest);
> +
> +                       if (dest == PTP_EV_PORT || dest == PTP_GEN_PORT)
> +                               padto = len + RTL_MIN_PATCH_LEN - trans_data_len;
> +               }
> +
> +               if (trans_data_len < UDP_HLEN)
> +                       padto = max(padto, len + UDP_HLEN - trans_data_len);
> +       }
> +
> +       return padto;
> +}
> +
> +static unsigned int rtl_quirk_packet_padto(struct rtl8169_private *tp,
> +                                          struct sk_buff *skb)
> +{
> +       unsigned int padto;
> +
> +       padto = rtl8125_quirk_udp_padto(tp, skb);
> +
>         switch (tp->mac_version) {
>         case RTL_GIGA_MAC_VER_34:
>         case RTL_GIGA_MAC_VER_60:
>         case RTL_GIGA_MAC_VER_61:
>         case RTL_GIGA_MAC_VER_63:
> -               return true;
> +               padto = max_t(unsigned int, padto, ETH_ZLEN);
>         default:
> -               return false;
> +               break;
>         }
> +
> +       return padto;
>  }
>
>  static void rtl8169_tso_csum_v1(struct sk_buff *skb, u32 *opts)
> @@ -4089,9 +4137,10 @@ static bool rtl8169_tso_csum_v2(struct rtl8169_private *tp,
>
>                 opts[1] |= transport_offset << TCPHO_SHIFT;
>         } else {
> -               if (unlikely(skb->len < ETH_ZLEN && rtl_test_hw_pad_bug(tp)))
> -                       /* eth_skb_pad would free the skb on error */
> -                       return !__skb_put_padto(skb, ETH_ZLEN, false);
> +               unsigned int padto = rtl_quirk_packet_padto(tp, skb);
> +
> +               /* skb_padto would free the skb on error */
> +               return !__skb_put_padto(skb, padto, false);
>         }
>
>         return true;
> @@ -4268,6 +4317,9 @@ static netdev_features_t rtl8169_features_check(struct sk_buff *skb,
>                 if (skb->len < ETH_ZLEN)
>                         features &= ~NETIF_F_CSUM_MASK;
>
> +               if (rtl_quirk_packet_padto(tp, skb))
> +                       features &= ~NETIF_F_CSUM_MASK;
> +
>                 if (transport_offset > TCPHO_MAX &&
>                     rtl_chip_supports_csum_v2(tp))
>                         features &= ~NETIF_F_CSUM_MASK;
> --
> 2.30.0
>