linux-kernel - Re: [PATCH v10] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6

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Message-ID: <CAMuHMdW16fs2rtHkwyGK_+Fhgi5LOFVYb6vPN4mTw3Fhjv1sqg@mail.gmail.com>
Date: Tue, 27 Feb 2024 12:17:58 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: Guenter Roeck <linux@...ck-us.net>, David Laight <David.Laight@...lab.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Helge Deller <deller@....de>, 
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>, 
	Parisc List <linux-parisc@...r.kernel.org>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, Arnd Bergmann <arnd@...db.de>, 
	linux-kernel@...r.kernel.org, Palmer Dabbelt <palmer@...osinc.com>
Subject: Re: [PATCH v10] lib: checksum: Use aligned accesses for ip_fast_csum
 and csum_ipv6_magic tests

Hi Charlie,

Thanks for your patch!

On Fri, Feb 23, 2024 at 11:12 PM Charlie Jenkins <charlie@...osinc.com> wrote:
> The test cases for ip_fast_csum and csum_ipv6_magic were not properly
> aligning the IP header, which were causing failures on architectures
> that do not support misaligned accesses like some ARM platforms. To
> solve this, align the data along (14 + NET_IP_ALIGN) bytes which is the
> standard alignment of an IP header and must be supported by the
> architecture.
>
> Furthermore, all architectures except the m68k pad "struct
> csum_ipv6_magic_data" to 44 bits. To make compatible with the m68k,
> manually pad this structure to 44 bits.

s/bits/bytes/ everywhere

>
> Fixes: 6f4c45cbcb00 ("kunit: Add tests for csum_ipv6_magic and ip_fast_csum")
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> Reviewed-by: Guenter Roeck <linux@...ck-us.net>
> Acked-by: Palmer Dabbelt <palmer@...osinc.com>
> ---
> The ip_fast_csum and csum_ipv6_magic tests did not work on all
> architectures due to differences in misaligned access support.
> Fix those issues by changing endianness of data and aligning the data.
>
> This patch relies upon a patch from Christophe:
>
> [PATCH net] kunit: Fix again checksum tests on big endian CPUs
>
> https://lore.kernel.org/lkml/73df3a9e95c2179119398ad1b4c84cdacbd8dfb6.1708684443.git.christophe.leroy@csgroup.eu/t/
> ---
> Changes in v10:
> - Christophe Leroy graciously decided to re-write my patch to fit his
>   style so I have dropped my endianness+sparse changes and have based by
>   alignment fixes on his patch. The link to his patch can be seen above.
> - I dropped Guenter's tested-by but kept his reviewed-by since only the base
>   was changed.
> - Link to v9: https://lore.kernel.org/r/20240221-fix_sparse_errors_checksum_tests-v9-0-bff4d73ab9d1@rivosinc.com

> --- a/lib/checksum_kunit.c
> +++ b/lib/checksum_kunit.c

> @@ -595,28 +473,31 @@ static void test_ip_fast_csum(struct kunit *test)
>  static void test_csum_ipv6_magic(struct kunit *test)
>  {
>  #if defined(CONFIG_NET)
> -       const struct in6_addr *saddr;
> -       const struct in6_addr *daddr;
> +       struct csum_ipv6_magic_data {
> +               const struct in6_addr saddr;
> +               const struct in6_addr daddr;
> +               __le32 len;
> +               __wsum csum;
> +               unsigned char proto;
> +               unsigned char pad[3];
> +       } *data;

If having a size of 44 bytes is critical, you really want to add a
BUILD_BUG_ON() check for that.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds