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

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Message-ID: <Y31fxXk/Ou3Zr6kS@monkey>
Date:   Tue, 22 Nov 2022 15:48:21 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        David Hildenbrand <david@...hat.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 11/22/22 15:03, Andrew Morton wrote:
> On Tue, 22 Nov 2022 13:59:25 -0400 Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > > > 
> > > >     While that's certainly valid, it's not the common use case with
> > > >     hugetlb pages.
> > > 
> > > FWIW, I did check with our product teams and they do not knowingly make use
> > > of private mappings without write.  Of course, that is only a small and
> > > limited sample size.
> > 
> > Yeah, if it is only this case I'm comfortable as well
> > 
> 
> So.... I am to slap a cc:stable on this patch and we're all good?

I think we will also need a Fixes tag.  There are two options for this:
1) In this patch David rightly points out
   "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."
   So, we could go with some old gup commit.
2) One of the benefits of this patch is silencing the warning introduced
   by 1d8d14641fd9 ("mm/hugetlb: support write-faults in shared mappings").
   So, we could use this for the tag.  It is also more in line with David's
   suggestion to "backport it into 6.0/6.1 to fix the warning".

My suggestion would be to use 1d8d14641fd9 for the fixes tag.  However,
David may have a better suggestion/idea.
-- 
Mike Kravetz