linux-kernel - Re: [PATCH 2/5] lib: add bitmap_{from,to}

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Message-ID: <YmvhLbIoHDhEhJFq@smile.fi.intel.com>
Date:   Fri, 29 Apr 2022 15:59:25 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Yury Norov <yury.norov@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 2/5] lib: add bitmap_{from,to}_arr64

On Thu, Apr 28, 2022 at 01:51:13PM -0700, Yury Norov wrote:
> Manipulating 64-bit arrays with bitmap functions is potentially dangerous
> because on 32-bit BE machines the order of halfwords doesn't match.
> Another issue is that compiler may throw a warning about out-of-boundary
> access.
> 
> This patch adds bitmap_{from,to}_arr64 functions in addition to existing
> bitmap_{from,to}_arr32.

...

> +	bitmap_copy_clear_tail((unsigned long *) (bitmap),	\
> +			(const unsigned long *) (buf), (nbits))

Drop spaces after castings. Besides that it might be placed on a single line.

...


> +	bitmap_copy_clear_tail((unsigned long *) (buf),		\
> +			(const unsigned long *) (bitmap), (nbits))

Ditto.

...

> +void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits)
> +{
> +	const unsigned long *end = bitmap + BITS_TO_LONGS(nbits);
> +
> +	while (bitmap < end) {
> +		*buf = *bitmap++;
> +		if (bitmap < end)
> +			*buf |= (u64)(*bitmap++) << 32;
> +		buf++;
> +	}
>  
> +	/* Clear tail bits in last element of array beyond nbits. */
> +	if (nbits % 64)
> +		buf[-1] &= GENMASK_ULL(nbits, 0);

Hmm... if nbits is > 0 and < 64, wouldn't be this problematic, since
end == bitmap? Or did I miss something?

> +}

-- 
With Best Regards,
Andy Shevchenko