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From:   Eric Dumazet <edumazet@google.com>
Date:   Wed, 24 Nov 2021 20:08:41 -0800
Message-ID: <CANn89i+edPKsp63R16kx4_kQ884ks=is8pg=W0wDbNV46UZ3vw@mail.gmail.com>
Subject: Re: [tip:x86/core 1/1] arch/x86/um/../lib/csum-partial_64.c:98:12:
 error: implicit declaration of function 'load_unaligned_zeropad'
To:     Noah Goldstein <goldstein.w.n@gmail.com>
Cc:     Johannes Berg <johannes@sipsolutions.net>, alexanderduyck@fb.com,
        kbuild-all@lists.01.org, open list <linux-kernel@vger.kernel.org>,
        linux-um@lists.infradead.org, lkp@intel.com, peterz@infradead.org,
        X86 ML <x86@kernel.org>
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On Wed, Nov 24, 2021 at 8:00 PM Eric Dumazet <edumazet@google.com> wrote:

>
> It is an issue in general, not in standard cases because network
> headers are aligned.
>
> I think it came when I folded csum_partial() and do_csum(), I forgot
> to ror() the seed.
>
> I suspect the following would help:
>
> diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
> index 1eb8f2d11f7c785be624eba315fe9ca7989fd56d..ee7b0e7a6055bcbef42d22f7e1d8f52ddbd6be6d
> 100644
> --- a/arch/x86/lib/csum-partial_64.c
> +++ b/arch/x86/lib/csum-partial_64.c
> @@ -41,6 +41,7 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
>         if (unlikely(odd)) {
>                 if (unlikely(len == 0))
>                         return sum;
> +               temp64 = ror32((__force u64)sum, 8);
>                 temp64 += (*(unsigned char *)buff << 8);
>                 len--;
>                 buff++;
>
>

It is a bit late here, I will test the following later this week.

We probably can remove one conditional jump at the end of the function

diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
index 1eb8f2d11f7c785be624eba315fe9ca7989fd56d..15986ad42ed5ccb8241ff467a34188cf901ec98e
100644
--- a/arch/x86/lib/csum-partial_64.c
+++ b/arch/x86/lib/csum-partial_64.c
@@ -41,9 +41,11 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
        if (unlikely(odd)) {
                if (unlikely(len == 0))
                        return sum;
+               temp64 = ror32((__force u64)sum, 8);
                temp64 += (*(unsigned char *)buff << 8);
                len--;
                buff++;
+               odd = 8;
        }

        while (unlikely(len >= 64)) {
@@ -129,10 +131,7 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
 #endif
        }
        result = add32_with_carry(temp64 >> 32, temp64 & 0xffffffff);
-       if (unlikely(odd)) {
-               result = from32to16(result);
-               result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
-       }
+       ror32(result, odd);
        return (__force __wsum)result;
 }
 EXPORT_SYMBOL(csum_partial);