linux-kernel - Re: [PATCH v2 1/3] userfaultfd: UFFDIO

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Message-ID: <27f177c9-1035-3277-cd62-dc81c12acec4@redhat.com>
Date:   Mon, 2 Oct 2023 16:42:50 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc:     viro@...iv.linux.org.uk, brauner@...nel.org, shuah@...nel.org,
        aarcange@...hat.com, lokeshgidra@...gle.com, peterx@...hat.com,
        hughd@...gle.com, mhocko@...e.com, axelrasmussen@...gle.com,
        rppt@...nel.org, willy@...radead.org, Liam.Howlett@...cle.com,
        jannh@...gle.com, zhangpeng362@...wei.com, bgeffon@...gle.com,
        kaleshsingh@...gle.com, ngeoffray@...gle.com, jdduke@...gle.com,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v2 1/3] userfaultfd: UFFDIO_REMAP: rmap preparation

On 23.09.23 03:31, Suren Baghdasaryan wrote:
> From: Andrea Arcangeli <aarcange@...hat.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