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Date:   Mon, 23 Oct 2023 17:53:23 +0200
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Subject: Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI
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From:   David Hildenbrand <david@redhat.com>
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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In-Reply-To: <721366d0-7909-45c9-ae49-f652c8369b9d@redhat.com>
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Precedence: bulk

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.

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

-- 
Cheers,

David / dhildenb