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Date:   Mon, 2 Oct 2023 16:42:50 +0200
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Subject: Re: [PATCH v2 1/3] userfaultfd: UFFDIO_REMAP: rmap preparation
To:     Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org
Cc:     viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org,
        aarcange@redhat.com, lokeshgidra@google.com, peterx@redhat.com,
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 <20230923013148.1390521-2-surenb@google.com>
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
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On 23.09.23 03:31, Suren Baghdasaryan wrote:
> From: Andrea Arcangeli <aarcange@redhat.com>
> 
> As far as the rmap code is concerned, UFFDIO_REMAP only alters the
> page->mapping and page->index. It does it while holding the page
> lock. However folio_referenced() is doing rmap walks without taking the
> folio lock first, so folio_lock_anon_vma_read() must be updated to
> re-check that the folio->mapping didn't change after we obtained the
> anon_vma read lock.

I'm curious: why don't we need this for existing users of 
page_move_anon_rmap()? What's special about UFFDIO_REMAP?


-- 
Cheers,

David / dhildenb