linux-kernel - Re: [PATCH 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200816040905.GF17456@casper.infradead.org>
Date:   Sun, 16 Aug 2020 05:09:05 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/pageblock: mitigation cmpxchg false sharing in
 pageblock flags

On Sun, Aug 16, 2020 at 11:47:56AM +0800, Alex Shi wrote:
> +++ b/mm/page_alloc.c
> @@ -467,6 +467,8 @@ static inline int pfn_to_bitidx(struct page *page, unsigned long pfn)
>  	return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
>  }
>  
> +#define BITS_PER_CHAR	8

include/linux/bits.h:#define BITS_PER_BYTE              8

>  	bitmap = get_pageblock_bitmap(page, pfn);
>  	bitidx = pfn_to_bitidx(page, pfn);
> -	word_bitidx = bitidx / BITS_PER_LONG;
> -	bitidx &= (BITS_PER_LONG-1);
> +	word_bitidx = bitidx / BITS_PER_CHAR;
> +	bitidx &= (BITS_PER_CHAR-1);

It's not a word any more.  it's a byte.