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Date: Mon, 25 Jan 2016 14:51:16 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Gerald Schaefer <gerald.schaefer@de.ibm.com>, linux-mm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] numa: fix /proc/<pid>/numa_maps for hugetlbfs on s390
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On Mon, 25 Jan 2016 17:30:42 +0100 Michael Holzheu <holzheu@linux.vnet.ibm.com> wrote:

> When working with hugetlbfs ptes (which are actually pmds) is not
> valid to directly use pte functions like pte_present() because the
> hardware bit layout of pmds and ptes can be different. This is the
> case on s390. Therefore we have to convert the hugetlbfs ptes first
> into a valid pte encoding with huge_ptep_get().
> 
> Currently the /proc/<pid>/numa_maps code uses hugetlbfs ptes without
> huge_ptep_get(). On s390 this leads to the following two problems:
> 
> 1) The pte_present() function returns false (instead of true) for
>    PROT_NONE hugetlb ptes. Therefore PROT_NONE vmas are missing
>    completely in the "numa_maps" output.
> 
> 2) The pte_dirty() function always returns false for all hugetlb ptes.
>    Therefore these pages are reported as "mapped=xxx" instead of
>    "dirty=xxx".
> 
> Therefore use huge_ptep_get() to correctly convert the hugetlb ptes.

I'm aiming this at 4.5 only.  Please let me know if you think that a
-stable backport is warranted.