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

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Message-Id: <20221121133320.a4e1c70af6ca72f29795fd5f@linux-foundation.org>
Date:   Mon, 21 Nov 2022 13:33:20 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Jason Gunthorpe <jgg@...dia.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.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 Mon, 21 Nov 2022 09:05:43 +0100 David Hildenbrand <david@...hat.com> wrote:

> >> 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.
> 
> With
> 
> https://lkml.kernel.org/r/20221116102659.70287-1-david@redhat.com
> 
> on it's way, the RDMA concern should be gone, hopefully.
> 
> @Andrew, can you queue this one? Thanks.

This is all a little tricky.

It's not good that 6.0 and earlier permit unprivileged userspace to
trigger a WARN.  But we cannot backport this fix into earlier kernels
because it requires the series "mm/gup: remove FOLL_FORCE usage from
drivers (reliable R/O long-term pinning)".

Is it possible to come up with a fix for 6.1 and earlier which won't
break RDMA?