linux-kernel - Re: [PATCH v2 2/4] mm: fail get_vaddr_frames() for filesystem-dax mappings

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Date:   Mon, 27 Nov 2017 08:19:59 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Inki Dae <inki.dae@...sung.com>, Linux MM <linux-mm@...ck.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Mel Gorman <mgorman@...e.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] mm: fail get_vaddr_frames() for filesystem-dax mappings

On Mon, Nov 27, 2017 at 8:15 AM, Jan Kara <jack@...e.cz> wrote:
> On Tue 14-11-17 11:56:39, Dan Williams wrote:
>> Until there is a solution to the dma-to-dax vs truncate problem it is
>> not safe to allow V4L2, Exynos, and other frame vector users to create
>> long standing / irrevocable memory registrations against filesytem-dax
>> vmas.
>>
>> Cc: Inki Dae <inki.dae@...sung.com>
>> Cc: Seung-Woo Kim <sw0312.kim@...sung.com>
>> Cc: Joonyoung Shim <jy0922.shim@...sung.com>
>> Cc: Kyungmin Park <kyungmin.park@...sung.com>
>> Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
>> Cc: linux-media@...r.kernel.org
>> Cc: Jan Kara <jack@...e.cz>
>> Cc: Mel Gorman <mgorman@...e.de>
>> Cc: Vlastimil Babka <vbabka@...e.cz>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: <stable@...r.kernel.org>
>> Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
>> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
>
> Makes sense. I'd just note that in principle get_vaddr_frames() is no more
> long-term than get_user_pages(). It is just so that all the users of
> get_vaddr_frames() currently want a long-term reference. Maybe could you
> add here also a comment that the vma_is_fsdax() check is there because all
> users of this function want a long term page reference? With that you can
> add:

Ok, will do.

> Reviewed-by: Jan Kara <jack@...e.cz>

Thanks.