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 t554Hx34 zcbC1qoaprrAWL0sD5e/EIl+ZvVV8hmG7Uk5klRZgob097F91KHWdApenAg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 01/04/23 23:19, James Houghton wrote: > PMD sharing can only be done in PUD_SIZE-aligned pieces of VMAs; > however, it is possible that HugeTLB VMAs are split without unsharing > the PMDs first. > > Without this fix, it is possible to hit the uffd-wp-related WARN_ON_ONCE > in hugetlb_change_protection [1]. The key there is that > hugetlb_unshare_all_pmds will not attempt to unshare PMDs in > non-PUD_SIZE-aligned sections of the VMA. > > It might seem ideal to unshare in hugetlb_vm_op_open, but we need to > unshare in both the new and old VMAs, so unsharing in > hugetlb_vm_op_split seems natural. > > [1]: https://lore.kernel.org/linux-mm/CADrL8HVeOkj0QH5VZZbRzybNE8CG-tEGFshnA+bG9nMgcWtBSg@mail.gmail.com/ > > Fixes: 6dfeaff93be1 ("hugetlb/userfaultfd: unshare all pmds for hugetlbfs when register wp") > Signed-off-by: James Houghton > --- > mm/hugetlb.c | 44 +++++++++++++++++++++++++++++++++++--------- > 1 file changed, 35 insertions(+), 9 deletions(-) Thanks for the updates and additional investigation, Reviewed-by: Mike Kravetz -- Mike Kravetz