mm/migrate_device.c: flush TLB while holding PTL

mm/migrate_device.c: flush TLB while holding PTL

When clearing a PTE the TLB should be flushed whilst still holding the PTL
to avoid a potential race with madvise/munmap/etc.  For example consider
the following sequence:

  CPU0                          CPU1
  ----                          ----

  migrate_vma_collect_pmd()
  pte_unmap_unlock()
                                madvise(MADV_DONTNEED)
                                -> zap_pte_range()
                                pte_offset_map_lock()
                                [ PTE not present, TLB not flushed ]
                                pte_unmap_unlock()
                                [ page is still accessible via stale TLB ]
  flush_tlb_range()

In this case the page may still be accessed via the stale TLB entry after
madvise returns.  Fix this by flushing the TLB while holding the PTL.

Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages")
Link: https://lkml.kernel.org/r/9f801e9d8d830408f2ca27821f606e09aa856899.1662078528.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple <[email protected]>
Reported-by: Nadav Amit <[email protected]>
Reviewed-by: "Huang, Ying" <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Acked-by: Peter Xu <[email protected]>
Cc: Alex Sierra <[email protected]>
Cc: Ben Skeggs <[email protected]>
Cc: Felix Kuehling <[email protected]>
Cc: huang ying <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Karol Herbst <[email protected]>
Cc: Logan Gunthorpe <[email protected]>
Cc: Lyude Paul <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ralph Campbell <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>