Re: [PATCH v2 1/3] userfaultfd: UFFDIO_REMAP: rmap preparation

[David Hildenbrand]

On 23.09.23 03:31, Suren Baghdasaryan wrote:
> From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
>
> As far as the rmap code is concerned, UFFDIO_REMAP only alters the
> page->mapping and page->index. It does it while holding the page
> lock. However folio_referenced() is doing rmap walks without taking the
> folio lock first, so folio_lock_anon_vma_read() must be updated to
> re-check that the folio->mapping didn't change after we obtained the
> anon_vma read lock.

I'm curious: why don't we need this for existing users of 
page_move_anon_rmap()? What's special about UFFDIO_REMAP?


--
Cheers,

David / dhildenb