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

On 27.01.2021 19:07, Willem de Bruijn wrote:

On Tue, Jan 26, 2021 at 2:40 PM Heiner Kallweit [off-list ref] wrote:

quoted

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 <redacted>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.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.

quoted

+       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?

quoted

+
+/* 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?

quoted

+               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)

quoted

+                       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

The workaround was provided by Realtek, I just modified it to match
mainline code style. For your reference I add the original version below.
I don't know where the magic numbers come from, Realtek releases
neither data sheets nor errata information.


#define MIN_PATCH_LEN (47)
static u32
rtl8125_get_patch_pad_len(struct sk_buff *skb)
{
        u32 pad_len = 0;
        int trans_data_len;
        u32 hdr_len;
        u32 pkt_len = skb->len;
        u8 ip_protocol;
        bool has_trans = skb_transport_header_was_set(skb);

        if (!(has_trans && (pkt_len < 175))) //128 + MIN_PATCH_LEN
                goto no_padding;

        ip_protocol = rtl8125_get_l4_protocol(skb);
        if (!(ip_protocol == IPPROTO_TCP || ip_protocol == IPPROTO_UDP))
                goto no_padding;

        trans_data_len = pkt_len -
                         (skb->transport_header -
                          skb_headroom(skb));
        if (ip_protocol == IPPROTO_UDP) {
                if (trans_data_len > 3 && trans_data_len < MIN_PATCH_LEN) {
                        u16 dest_port = 0;

                        skb_copy_bits(skb, skb->transport_header - skb_headroom(skb) + 2, &dest_port, 2);
                        dest_port = ntohs(dest_port);

                        if (dest_port == 0x13f ||
                            dest_port == 0x140) {
                                pad_len = MIN_PATCH_LEN - trans_data_len;
                                goto out;
                        }
                }
        }

        hdr_len = 0;
        if (ip_protocol == IPPROTO_TCP)
                hdr_len = 20;
        else if (ip_protocol == IPPROTO_UDP)
                hdr_len = 8;
        if (trans_data_len < hdr_len)
                pad_len = hdr_len - trans_data_len;

out:
        if ((pkt_len + pad_len) < ETH_ZLEN)
                pad_len = ETH_ZLEN - pkt_len;

        return pad_len;

no_padding:

        return 0;
}