linux-kernel - Re: [PATCH RESEND2] lib: fix bitmap_parse() on 64-bit big endian archs

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Message-ID: <CAHp75VcFdrvNMj0TL8ZHxShqqGDM31Hy8vitmn9HOPjZ6f9uYw@mail.gmail.com>
Date:   Mon, 8 Jun 2020 15:03:05 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Alexander Gordeev <agordeev@...ux.ibm.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-s390@...r.kernel.org, Stable <stable@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Amritha Nambiar <amritha.nambiar@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        "Tobin C . Harding" <tobin@...nel.org>,
        Vineet Gupta <vineet.gupta1@...opsys.com>,
        Will Deacon <will.deacon@....com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH RESEND2] lib: fix bitmap_parse() on 64-bit big endian archs

On Mon, Jun 8, 2020 at 1:26 PM Alexander Gordeev <agordeev@...ux.ibm.com> wrote:
>
> Commit 2d6261583be0 ("lib: rework bitmap_parse()") does not
> take into account order of halfwords on 64-bit big endian
> architectures. As result (at least) Receive Packet Steering,
> IRQ affinity masks and runtime kernel test "test_bitmap" get
> broken on s390.

...

> +#if defined(__BIG_ENDIAN) && defined(CONFIG_64BIT)

I think it's better to re-use existing patterns.

ipc/sem.c:1682:#if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)

> +static void save_x32_chunk(unsigned long *maskp, u32 chunk, int chunk_idx)
> +{
> +       maskp += (chunk_idx / 2);
> +       ((u32 *)maskp)[(chunk_idx & 1) ^ 1] = chunk;
> +}
> +#else
> +static void save_x32_chunk(unsigned long *maskp, u32 chunk, int chunk_idx)
> +{
> +       ((u32 *)maskp)[chunk_idx] = chunk;
> +}
> +#endif

See below.

...

> -               end = bitmap_get_x32_reverse(start, end, bitmap++);
> +               end = bitmap_get_x32_reverse(start, end, &chunk);
>                 if (IS_ERR(end))
>                         return PTR_ERR(end);
> +
> +               save_x32_chunk(maskp, chunk, chunk_idx++);

Can't we simple do

        int chunk_index = 0;
        ...
        do {
#if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)
               end = bitmap_get_x32_reverse(start, end,
bitmap[chunk_index ^ 1]);
#else
               end = bitmap_get_x32_reverse(start, end, bitmap[chunk_index]);
#endif
        ...
        } while (++chunk_index);

?

-- 
With Best Regards,
Andy Shevchenko