Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding new mmap flags

From	Dan Williams <dan.j.williams@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding new mmap flags
Date	2017-09-18 17:50 +0200
Message-ID	<ur6t4-88P-31@gated-at.bofh.it> (permalink)
References	(1 earlier) <ueDmN-68s-9@gated-at.bofh.it> <ueJ8R-1g7-9@gated-at.bofh.it> <uqyKJ-2tz-1@gated-at.bofh.it> <uqLHY-2yS-5@gated-at.bofh.it> <ur0H1-4j6-43@gated-at.bofh.it>
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On Mon, Sep 18, 2017 at 2:31 AM, Jan Kara <jack@suse.cz> wrote:
> On Sun 17-09-17 19:39:45, Christoph Hellwig wrote:
>> On Sat, Sep 16, 2017 at 08:44:14PM -0700, Dan Williams wrote:
>> > So it wasn't all that easy, and Linus declined to take it. I think we
>> > should add a new ->mmap_validate() file operation and save the
>> > tree-wide cleanup until later.
>>
>> Note that we already have a mmap_capabilities callout for nommu,
>> I wonder if we could generalize that.
>
> So if I understood Dan right, Linus refused to merge the patch which adds
> 'flags' argument to ->mmap callback. That is actually logically independent
> change from validating flags passed to mmap(2) syscall. Dan did it just to
> save himself from adding a VMA flag for MAP_DIRECT.
>
> For validating flags passed to mmap(2), I agree we could use
> ->mmap_capabilities() instead of mmap_supported_mask Dan has added. But I
> don't have a strong opinion there.

The drawback I see with mmap_capabilities is that it requires all mmap
flags to have a corresponding vm_flag. After the cold reaction the
VM_DAX flag received I'd want to be sure they were on board with this
direction.

Thread

Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding  new mmap flags Dan Williams <dan.j.williams@intel.com> - 2017-09-17 05:50 +0200
  Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for         adding new mmap flags Christoph Hellwig <hch@lst.de> - 2017-09-17 19:40 +0200
    Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding  new mmap flags Jan Kara <jack@suse.cz> - 2017-09-18 11:40 +0200
      Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding  new mmap flags Dan Williams <dan.j.williams@intel.com> - 2017-09-18 17:50 +0200
  Re: [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding  new mmap flags Jan Kara <jack@suse.cz> - 2017-09-18 11:30 +0200

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