Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI

[Suren Baghdasaryan]

On Mon, Oct 23, 2023 at 8:53 AM David Hildenbrand <david@xxxxxxxxxx> 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) != (dst_vma->vm_flags & VM_LOCKED))
> >> +            return -EINVAL;
> >> +
> >> +    if (!(src_vma->vm_flags & VM_WRITE) || !(dst_vma->vm_flags & VM_WRITE))
> >> +            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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