linux-kernel - Re: [patch] mmap.2: document the munmap exception for underlying page size

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: <55AFD009.6080706@gmail.com>
Date:	Wed, 22 Jul 2015 19:16:57 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	mtk.manpages@...il.com, Hugh Dickins <hughd@...gle.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Eric B Munson <emunson@...mai.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-man@...r.kernel.org
Subject: Re: [patch] mmap.2: document the munmap exception for underlying
 page size

Hi David,

On 07/22/2015 02:41 AM, David Rientjes wrote:
> munmap(2) will fail with an errno of EINVAL for hugetlb memory if the 
> length is not a multiple of the underlying page size.
> 
> Documentation/vm/hugetlbpage.txt was updated to specify this behavior 
> since Linux 4.1 in commit 80d6b94bd69a ("mm, doc: cleanup and clarify 
> munmap behavior for hugetlb memory").
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  man2/mmap.2 | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/man2/mmap.2 b/man2/mmap.2
> --- a/man2/mmap.2
> +++ b/man2/mmap.2
> @@ -383,6 +383,10 @@ All pages containing a part
>  of the indicated range are unmapped, and subsequent references
>  to these pages will generate
>  .BR SIGSEGV .
> +An exception is when the underlying memory is not of the native page
> +size, such as hugetlb page sizes, whereas
> +.I length
> +must be a multiple of the underlying page size.
>  It is not an error if the
>  indicated range does not contain any mapped pages.
>  .SS Timestamps changes for file-backed mappings

I'm struggling a bit to understand your text. Is the point this:

    If we have a hugetlb area, then the munmap() length
    must be a multiple of the page size.

?

Are there any requirements about 'addr'? Must it also me huge-page-aligned?

Thanks,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/