linux-kernel - Re: [PATCH v3 2/3] userfaultfd: UFFDIO

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Message-ID: <045c35ba-7872-40a7-bd86-e37771076b88@redhat.com>
Date:   Mon, 23 Oct 2023 17:53:23 +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 v3 2/3] userfaultfd: UFFDIO_MOVE uABI

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