linux-kernel - Re: [PATCH v1] mm/gup: disallow FOLL_FORCE|FOLL

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Message-ID: <Y2BIbyxT0Bh6bCUr@monkey>
Date:   Mon, 31 Oct 2022 15:13:03 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        syzbot+f0b97304ef90f0d0b1dc@...kaller.appspotmail.com
Subject: Re: [PATCH v1] mm/gup: disallow FOLL_FORCE|FOLL_WRITE on hugetlb
 mappings

On 10/31/22 13:14, Jason Gunthorpe wrote:
> On Mon, Oct 31, 2022 at 04:25:24PM +0100, David Hildenbrand wrote:
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Mike Kravetz <mike.kravetz@...cle.com>
> > Cc: Peter Xu <peterx@...hat.com>
> > Cc: John Hubbard <jhubbard@...dia.com>
> > Cc: Jason Gunthorpe <jgg@...dia.com>
> > Reported-by: syzbot+f0b97304ef90f0d0b1dc@...kaller.appspotmail.com
> > Signed-off-by: David Hildenbrand <david@...hat.com>
> > ---
> > 
> > I assume this has been broken at least since 2014, when mm/gup.c came to
> > life. I failed to come up with a suitable Fixes tag quickly.
> 
> I'm worried this would break RDMA over hugetlbfs maps - which is a
> real thing people do.

Yes, it is a real thing.  Unfortunately, I do not know exactly how it is used.

> 
> MikeK do you have test cases?

Sorry, I do not have any test cases.

I can ask one of our product groups about their usage.  But, that would
certainly not be a comprehensive view.
-- 
Mike Kravetz