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From:   James Houghton <jthoughton@google.com>
Date:   Tue, 3 Jan 2023 20:27:34 +0000
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Subject: Re: [PATCH] hugetlb: unshare some PMDs when splitting VMAs
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Muchun Song <songmuchun@bytedance.com>,
        Peter Xu <peterx@redhat.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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> I think I've come up with one... :) It only took many many hours of
> staring at code to come up with:
>
> 1. Fault in PUD_SIZE-aligned hugetlb mapping
> 2. fork() (to actually share the PMDs)

Erm, I mean: mmap(), then fork(), then fault in both processes.