Re: [PATCH] mm: userfaultfd: fix unexpected change to src_folio when UFFDIO_MOVE fails

[Andrew Morton]

On Thu, 22 Feb 2024 16:08:15 +0800 Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:

> After ptep_clear_flush(), if we find that src_folio is pinned we will fail
> UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
> src_folio->{mapping,index} is not restored in this process. This is not
> what we expected, so fix it.
> 
> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")

What are the expected worst-case userspace-visible runtime effects of
this flaw?