mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race

huge_pmd_unshare() drops a reference on a page table that may have
previously been shared across processes, potentially turning it into a
normal page table used in another process in which unrelated VMAs can
afterwards be installed.

If this happens in the middle of a concurrent gup_fast(), gup_fast() could
end up walking the page tables of another process.  While I don't see any
way in which that immediately leads to kernel memory corruption, it is
really weird and unexpected.

Fix it with an explicit broadcast IPI through tlb_remove_table_sync_one(),
just like we do in khugepaged when removing page tables for a THP
collapse.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 39dde65c9940 ("[PATCH] shared page table for hugetlb page")
Signed-off-by: Jann Horn <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions