linux-kernel - Re: [PATCH v2 2/3] userfaultfd: UFFDIO

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Message-ID: <ZRWpwx1N3ucnrrFE@x1n>
Date:   Thu, 28 Sep 2023 12:28:51 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     David Hildenbrand <david@...hat.com>, Jann Horn <jannh@...gle.com>,
        akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
        brauner@...nel.org, shuah@...nel.org, aarcange@...hat.com,
        lokeshgidra@...gle.com, hughd@...gle.com, mhocko@...e.com,
        axelrasmussen@...gle.com, rppt@...nel.org, willy@...radead.org,
        Liam.Howlett@...cle.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 2/3] userfaultfd: UFFDIO_REMAP uABI

On Wed, Sep 27, 2023 at 11:25:22AM -0700, Suren Baghdasaryan wrote:
> For uffd_remap can_change_pte_writable() would fail it VM_WRITE is not
> set, but we want remapping to work for RO memory as well.

Is there an use case that we want remap to work on RO?

The thing is, either removing a page or installing a new one with valid
content imply VM_WRITE to me on either side..

Thanks,

-- 
Peter Xu