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Date:   Thu, 28 Sep 2023 12:24:53 -0400
From:   Peter Xu <peterx@redhat.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     Jann Horn <jannh@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        akpm@linux-foundation.org, viro@zeniv.linux.org.uk,
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        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, kernel-team@android.com
Subject: Re: [PATCH v2 2/3] userfaultfd: UFFDIO_REMAP uABI
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On Wed, Sep 27, 2023 at 03:29:35PM +0200, David Hildenbrand wrote:
> > > +       if (!pte_same(*src_pte, orig_src_pte) ||
> > > +           !pte_same(*dst_pte, orig_dst_pte) ||
> > > +           folio_test_large(src_folio) ||
> > > +           folio_estimated_sharers(src_folio) != 1) {
> 
> ^ here you should check PageAnonExclusive. Please get rid of any implicit
> explicit/implcit mapcount checks.

David, is PageAnon 100% accurate now in the current tree?

IOW, can it be possible that the page has total_mapcount==1 but missing
AnonExclusive bit in any possible way?

Thanks,

-- 
Peter Xu