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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Mon, 23 Oct 2023 12:00:09 -0700
Message-ID: <CAJuCfpH8oare_erzHuhiV0knbwVEmOzq6DnoywNQpOCAqJMucA@mail.gmail.com>
Subject: Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI
To:     David Hildenbrand <david@redhat.com>
Cc:     akpm@linux-foundation.org, viro@zeniv.linux.org.uk,
        brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com,
        lokeshgidra@google.com, peterx@redhat.com, hughd@google.com,
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        willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com,
        zhangpeng362@huawei.com, bgeffon@google.com,
        kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        kernel-team@android.com
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On Mon, Oct 23, 2023 at 8:53=E2=80=AFAM David Hildenbrand <david@redhat.com=
> wrote:
>
> On 23.10.23 14:29, David Hildenbrand wrote:
> >> +
> >> +    /* Only allow remapping if both are mlocked or both aren't */
> >> +    if ((src_vma->vm_flags & VM_LOCKED) !=3D (dst_vma->vm_flags & VM_=
LOCKED))
> >> +            return -EINVAL;
> >> +
> >> +    if (!(src_vma->vm_flags & VM_WRITE) || !(dst_vma->vm_flags & VM_W=
RITE))
> >> +            return -EINVAL;
> >
> > Why does one of both need VM_WRITE? If one really needs it, then the
> > destination (where we're moving stuff to).
>
> Just realized that we want both to be writable.
>
> If you have this in place, there is no need to use maybe*_mkwrite(), you
> can use the non-maybe variants.

Ack.

>
> I recall that for UFFDIO_COPY we even support PROT_NONE VMAs, is there
> any reason why we want to have different semantics here?

I don't think so. At least not for the single-mm case.

>
> --
> Cheers,
>
> David / dhildenb
>
> --
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