target/linux/generic/backport-5.4/050-gro-fix-napi_gro_frags-Fast-GRO-breakage-due-to-IP-a.patch

   1 From 3007b05df4301aad179acc6ca1c3645785576df6 Mon Sep 17 00:00:00 2001
   2 From: Alexander Lobakin <alobakin@pm.me>
   3 Date: Mon, 19 Apr 2021 12:53:06 +0000
   4 Subject: gro: fix napi_gro_frags() Fast GRO breakage due to IP
   5  alignment check
   6
   7 Commit 7ad18ff6449cbd6beb26b53128ddf56d2685aa93 upstream.
   8
   9 Commit 38ec4944b593 ("gro: ensure frag0 meets IP header alignment")
  10 did the right thing, but missed the fact that napi_gro_frags() logics
  11 calls for skb_gro_reset_offset() *before* pulling Ethernet header
  12 to the skb linear space.
  13 That said, the introduced check for frag0 address being aligned to 4
  14 always fails for it as Ethernet header is obviously 14 bytes long,
  15 and in case with NET_IP_ALIGN its start is not aligned to 4.
  16
  17 Fix this by adding @nhoff argument to skb_gro_reset_offset() which
  18 tells if an IP header is placed right at the start of frag0 or not.
  19 This restores Fast GRO for napi_gro_frags() that became very slow
  20 after the mentioned commit, and preserves the introduced check to
  21 avoid silent unaligned accesses.
  22
  23 From v1 [0]:
  24  - inline tiny skb_gro_reset_offset() to let the code be optimized
  25    more efficively (esp. for the !NET_IP_ALIGN case) (Eric);
  26  - pull in Reviewed-by from Eric.
  27
  28 [0] https://lore.kernel.org/netdev/20210418114200.5839-1-alobakin@pm.me
  29
  30 Fixes: 38ec4944b593 ("gro: ensure frag0 meets IP header alignment")
  31 Reviewed-by: Eric Dumazet <edumazet@google.com>
  32 Signed-off-by: Alexander Lobakin <alobakin@pm.me>
  33 Signed-off-by: David S. Miller <davem@davemloft.net>
  34 ---
  35  net/core/dev.c | 8 ++++----
  36  1 file changed, 4 insertions(+), 4 deletions(-)
  37
  38 --- a/net/core/dev.c
  39 +++ b/net/core/dev.c
  40 @@ -5395,7 +5395,7 @@ static struct list_head *gro_list_prepar
  41         return head;
  42  }
  43
  44 -static void skb_gro_reset_offset(struct sk_buff *skb)
  45 +static inline void skb_gro_reset_offset(struct sk_buff *skb, u32 nhoff)
  46  {
  47         const struct skb_shared_info *pinfo = skb_shinfo(skb);
  48         const skb_frag_t *frag0 = &pinfo->frags[0];
  49 @@ -5407,7 +5407,7 @@ static void skb_gro_reset_offset(struct
  50         if (skb_mac_header(skb) == skb_tail_pointer(skb) &&
  51             pinfo->nr_frags &&
  52             !PageHighMem(skb_frag_page(frag0)) &&
  53 -           (!NET_IP_ALIGN || !(skb_frag_off(frag0) & 3))) {
  54 +           (!NET_IP_ALIGN || !((skb_frag_off(frag0) + nhoff) & 3))) {
  55                 NAPI_GRO_CB(skb)->frag0 = skb_frag_address(frag0);
  56                 NAPI_GRO_CB(skb)->frag0_len = min_t(unsigned int,
  57                                                     skb_frag_size(frag0),
  58 @@ -5640,7 +5640,7 @@ gro_result_t napi_gro_receive(struct nap
  59         skb_mark_napi_id(skb, napi);
  60         trace_napi_gro_receive_entry(skb);
  61
  62 -       skb_gro_reset_offset(skb);
  63 +       skb_gro_reset_offset(skb, 0);
  64
  65         ret = napi_skb_finish(napi, skb, dev_gro_receive(napi, skb));
  66         trace_napi_gro_receive_exit(ret);
  67 @@ -5733,7 +5733,7 @@ static struct sk_buff *napi_frags_skb(st
  68         napi->skb = NULL;
  69
  70         skb_reset_mac_header(skb);
  71 -       skb_gro_reset_offset(skb);
  72 +       skb_gro_reset_offset(skb, hlen);
  73
  74         if (unlikely(skb_gro_header_hard(skb, hlen))) {
  75                 eth = skb_gro_header_slow(skb, hlen, 0);