Re: [PATCH v3 net] r8169: work around RTL8125 UDP hw bug

On 28.01.2021 19:36, Willem de Bruijn wrote:

On Thu, Jan 28, 2021 at 2:44 AM 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

v2:
- rebased to net
v3:
- make rtl_skb_is_udp() more robust and use skb_header_pointer()
  to access the ip(v6) header

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 | 70 +++++++++++++++++++++--
 1 file changed, 64 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index a569abe7f..457fa1404 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>

this is only for UDP_HLEN? perhaps use sizeof(struct udphdr) instead
to remove the dependency.

It's also for PTP_EV_PORT. But yes, we can define this locally to
remove the dependency.

quoted

 #include <net/ip6_checksum.h>

 #include "r8169.h"

@@ -4046,17 +4047,70 @@ 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)
 {
+       int no = skb_network_offset(skb);
+       struct ipv6hdr *i6h, _i6h;
+       struct iphdr *ih, _ih;
+
+       switch (vlan_get_protocol(skb)) {
+       case htons(ETH_P_IP):
+               ih = skb_header_pointer(skb, no, sizeof(_ih), &_ih);
+               return ih && ih->protocol == IPPROTO_UDP;
+       case htons(ETH_P_IPV6):
+               i6h = skb_header_pointer(skb, no, sizeof(_i6h), &_i6h);
+               return i6h && i6h->nexthdr == IPPROTO_UDP;
+       default:
+               return false;
+       }
+}
+
+#define RTL_MIN_PATCH_LEN      47
+#define PTP_GEN_PORT           320
+
+/* 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 < 128 + RTL_MIN_PATCH_LEN &&
+           rtl_skb_is_udp(skb) && skb_transport_header_was_set(skb)) {
+               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) {

   trans_data_len > 3

here probably means

   trans_data_len >= offsetof(struct udphdr, len)

offsetof(struct udphdr, len) = 5
Presumably the check ensures that udphdr->dest is accessible. I think we should
use skb_header_pointer() here too.

to safely access dest. Then that is a bit more self documenting

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)

nit: else if ?

I don't think so. If e.g. trans_data_len == 5 and dest port isn't a PTP port,
then the trans_data_len < UDP_HLEN branch wouldn't be execeuted.

quoted

+                       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)

@@ -4128,9 +4182,10 @@ 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);

should this path still pad to ETH_ZLEN as a minimum when the other
cases do not hit?

For most chip versions that's not needed because hw does the padding
to ETH_ZLEN. Few chip versions have a hw bug and padding needs to be
done in sw, that's handled in rtl_quirk_packet_padto().

quoted

        }

        return true;

@@ -4307,6 +4362,9 @@ 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