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

On 23.09.23 03:31, Suren Baghdasaryan wrote:

From: Andrea Arcangeli aarcange@redhat.com

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?