On Wed, Nov 24, 2021 at 10:20 PM Eric Dumazet [off-list ref] wrote:

On Wed, Nov 24, 2021 at 8:08 PM Eric Dumazet [off-list ref] wrote:

quoted

On Wed, Nov 24, 2021 at 8:00 PM Eric Dumazet [off-list ref] wrote:

quoted

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.

quoted

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

All my tests pass with that change :)

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