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@@ -0,0 +1,75 @@
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+From 3007b05df4301aad179acc6ca1c3645785576df6 Mon Sep 17 00:00:00 2001
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+From: Alexander Lobakin <[email protected]>
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+Date: Mon, 19 Apr 2021 12:53:06 +0000
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+Subject: gro: fix napi_gro_frags() Fast GRO breakage due to IP
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+ alignment check
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+
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+Commit 7ad18ff6449cbd6beb26b53128ddf56d2685aa93 upstream.
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+
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+Commit 38ec4944b593 ("gro: ensure frag0 meets IP header alignment")
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+did the right thing, but missed the fact that napi_gro_frags() logics
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+calls for skb_gro_reset_offset() *before* pulling Ethernet header
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+to the skb linear space.
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+That said, the introduced check for frag0 address being aligned to 4
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+always fails for it as Ethernet header is obviously 14 bytes long,
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+and in case with NET_IP_ALIGN its start is not aligned to 4.
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+
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+Fix this by adding @nhoff argument to skb_gro_reset_offset() which
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+tells if an IP header is placed right at the start of frag0 or not.
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+This restores Fast GRO for napi_gro_frags() that became very slow
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+after the mentioned commit, and preserves the introduced check to
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+avoid silent unaligned accesses.
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+
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+From v1 [0]:
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+ - inline tiny skb_gro_reset_offset() to let the code be optimized
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+ more efficively (esp. for the !NET_IP_ALIGN case) (Eric);
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+ - pull in Reviewed-by from Eric.
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+
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+[0] https://lore.kernel.org/netdev/[email protected]
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+
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+Fixes: 38ec4944b593 ("gro: ensure frag0 meets IP header alignment")
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+Reviewed-by: Eric Dumazet <[email protected]>
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+Signed-off-by: Alexander Lobakin <[email protected]>
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+Signed-off-by: David S. Miller <[email protected]>
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+---
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+ net/core/dev.c | 8 ++++----
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+ 1 file changed, 4 insertions(+), 4 deletions(-)
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+
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+--- a/net/core/dev.c
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++++ b/net/core/dev.c
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+@@ -5395,7 +5395,7 @@ static struct list_head *gro_list_prepar
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+ return head;
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+ }
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+
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+-static void skb_gro_reset_offset(struct sk_buff *skb)
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++static inline void skb_gro_reset_offset(struct sk_buff *skb, u32 nhoff)
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+ {
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+ const struct skb_shared_info *pinfo = skb_shinfo(skb);
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+ const skb_frag_t *frag0 = &pinfo->frags[0];
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+@@ -5407,7 +5407,7 @@ static void skb_gro_reset_offset(struct
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+ if (skb_mac_header(skb) == skb_tail_pointer(skb) &&
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+ pinfo->nr_frags &&
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+ !PageHighMem(skb_frag_page(frag0)) &&
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+- (!NET_IP_ALIGN || !(skb_frag_off(frag0) & 3))) {
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++ (!NET_IP_ALIGN || !((skb_frag_off(frag0) + nhoff) & 3))) {
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+ NAPI_GRO_CB(skb)->frag0 = skb_frag_address(frag0);
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+ NAPI_GRO_CB(skb)->frag0_len = min_t(unsigned int,
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+ skb_frag_size(frag0),
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+@@ -5640,7 +5640,7 @@ gro_result_t napi_gro_receive(struct nap
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+ skb_mark_napi_id(skb, napi);
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+ trace_napi_gro_receive_entry(skb);
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+
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+- skb_gro_reset_offset(skb);
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++ skb_gro_reset_offset(skb, 0);
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+
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+ ret = napi_skb_finish(napi, skb, dev_gro_receive(napi, skb));
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+ trace_napi_gro_receive_exit(ret);
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+@@ -5733,7 +5733,7 @@ static struct sk_buff *napi_frags_skb(st
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+ napi->skb = NULL;
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+
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+ skb_reset_mac_header(skb);
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+- skb_gro_reset_offset(skb);
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++ skb_gro_reset_offset(skb, hlen);
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+
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+ if (unlikely(skb_gro_header_hard(skb, hlen))) {
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+ eth = skb_gro_header_slow(skb, hlen, 0);
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