On Wed, Nov 24, 2021 at 8:08 PM Eric Dumazet <edumazet@google.com> wrote:
>
> 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);

this would be
          result = ror32(result, odd);

definitely time to stop working today for me.

>         return (__force __wsum)result;
>  }
>  EXPORT_SYMBOL(csum_partial);