linux-kernel - RE: x86/csum: Remove unnecessary odd handling

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Message-ID: <5b04b05ecd3e4111bb12ac0c7317933e@AcuMS.aculab.com>
Date:   Thu, 29 Jun 2023 14:27:55 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Borislav Petkov' <bp@...en8.de>,
        Noah Goldstein <goldstein.w.n@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        lkml <linux-kernel@...r.kernel.org>
Subject: RE: x86/csum: Remove unnecessary odd handling

...
> > All csum kunit tests pass.

Last time I looked I couldn't see where generated IPv6
checksums get changed from 0x0000 (from ~csum_fold() using
adc) to 0xffff - which I think the protocol requires.

The trivial way to do this is to initialise the sum to 1
(instead or 0 or 0xffff) and then add 1 after the invert.

It doesn't matter (much) for IPv4 because 0x0000 is 'no checksum'
rather than 'invalid'.

	David

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