This is v5 of uffd-wp shmem & hugetlbfs support, which completes uffd-wp as a full feature. It's based on v5.14-rc1. I reposted the whole series majorly to trigger the syzbot tests again; sorry if it brings a bit of noise. Please let me know if there's easier way to trigger the syzbot test instead of reposting the whole series. Meanwhile, recently discussion around soft-dirty shows that soft-dirty may have similar requirement as uffd-wp on persisting the dirty information: https://lore.kernel.org/lkml/20210714152426.216217-1-tiberiu.georgescu@xxxxxxxxxxx/ Then the mechanism provided in this patchset may be suitable for soft-dirty too. The whole series can also be found online [1]. v5 changelog: - Fix two issues spotted by syzbot - Compile test with (1) !USERFAULTFD, (2) USERFAULTFD && !USERFAULTFD_WP Previous versions: RFC: https://lore.kernel.org/lkml/20210115170907.24498-1-peterx@xxxxxxxxxx/ v1: https://lore.kernel.org/lkml/20210323004912.35132-1-peterx@xxxxxxxxxx/ v2: https://lore.kernel.org/lkml/20210427161317.50682-1-peterx@xxxxxxxxxx/ v3: https://lore.kernel.org/lkml/20210527201927.29586-1-peterx@xxxxxxxxxx/ v4: https://lore.kernel.org/lkml/20210714222117.47648-1-peterx@xxxxxxxxxx/ About Swap Special PTE ====================== In short, the so-called "swap special pte" in this patchset is a new type of pte that doesn't exist in the past, but it got used initially in this series in file-backed memories. It is used to persist information even if the ptes got dropped meanwhile when the page cache still existed. For example, when splitting a file-backed huge pmd, we could be simply dropping the pmd entry then wait until another fault coming. It's okay in the past since all information in the pte can be retained from the page cache when the next page fault triggers. However in this case, uffd-wp is per-pte information which cannot be kept in page cache, so that information needs to be maintained somehow still in the pgtable entry, even if the pgtable entry is going to be dropped. Here instead of replacing with a none entry, we used the "swap special pte". Then when the next page fault triggers, we can observe orig_pte to retain this information. I'm copy-pasting some commit message from the patch "mm/swap: Introduce the idea of special swap ptes", where it tried to explain this pte in another angle: We used to have special swap entries, like migration entries, hw-poison entries, device private entries, etc. Those "special swap entries" reside in the range that they need to be at least swap entries first, and their types are decided by swp_type(entry). This patch introduces another idea called "special swap ptes". It's very easy to get confused against "special swap entries", but a speical swap pte should never contain a swap entry at all. It means, it's illegal to call pte_to_swp_entry() upon a special swap pte. Make the uffd-wp special pte to be the first special swap pte. Before this patch, is_swap_pte()==true means one of the below: (a.1) The pte has a normal swap entry (non_swap_entry()==false). For example, when an anonymous page got swapped out. (a.2) The pte has a special swap entry (non_swap_entry()==true). For example, a migration entry, a hw-poison entry, etc. After this patch, is_swap_pte()==true means one of the below, where case (b) is added: (a) The pte contains a swap entry. (a.1) The pte has a normal swap entry (non_swap_entry()==false). For example, when an anonymous page got swapped out. (a.2) The pte has a special swap entry (non_swap_entry()==true). For example, a migration entry, a hw-poison entry, etc. (b) The pte does not contain a swap entry at all (so it cannot be passed into pte_to_swp_entry()). For example, uffd-wp special swap pte. Hugetlbfs needs similar thing because it's also file-backed. I directly reused the same special pte there, though the shmem/hugetlb change on supporting this new pte is different since they don't share code path a lot. Patch layout ============ Part (1): Shmem support, this is where the special swap pte is introduced. Some zap rework is needed within the process: mm/shmem: Unconditionally set pte dirty in mfill_atomic_install_pte shmem/userfaultfd: Take care of UFFDIO_COPY_MODE_WP mm: Clear vmf->pte after pte_unmap_same() returns mm/userfaultfd: Introduce special pte for unmapped file-backed mem mm/swap: Introduce the idea of special swap ptes shmem/userfaultfd: Handle uffd-wp special pte in page fault handler mm: Drop first_index/last_index in zap_details mm: Introduce zap_details.zap_flags mm: Introduce ZAP_FLAG_SKIP_SWAP shmem/userfaultfd: Persist uffd-wp bit across zapping for file-backed shmem/userfaultfd: Allow wr-protect none pte for file-backed mem shmem/userfaultfd: Allows file-back mem to be uffd wr-protected on thps shmem/userfaultfd: Handle the left-overed special swap ptes shmem/userfaultfd: Pass over uffd-wp special swap pte when fork() Part (2): Hugetlb supportdisable huge pmd sharing for uffd-wp patches have been merged. The rest is the changes required to teach hugetlbfs understand the special swap pte too that introduced with the uffd-wp change: mm/hugetlb: Drop __unmap_hugepage_range definition from hugetlb.h mm/hugetlb: Introduce huge pte version of uffd-wp helpers hugetlb/userfaultfd: Hook page faults for uffd write protection hugetlb/userfaultfd: Take care of UFFDIO_COPY_MODE_WP hugetlb/userfaultfd: Handle UFFDIO_WRITEPROTECT mm/hugetlb: Introduce huge version of special swap pte helpers hugetlb/userfaultfd: Handle uffd-wp special pte in hugetlb pf handler hugetlb/userfaultfd: Allow wr-protect none ptes hugetlb/userfaultfd: Only drop uffd-wp special pte if required Part (3): Enable both features in code and test (plus pagemap support) mm/pagemap: Recognize uffd-wp bit for shmem/hugetlbfs userfaultfd: Enable write protection for shmem & hugetlbfs userfaultfd/selftests: Enable uffd-wp for shmem/hugetlbfs Tests ===== I've tested it using either userfaultfd kselftest program, but also with umapsort [2] which should be even stricter. Tested page swapping in/out during umapsort. If anyone would like to try umapsort, need to use an extremely hacked version of umap library [3], because by default umap only supports anonymous. So to test it we need to build [3] then [2]. Any comment would be greatly welcomed. Thanks, [1] https://github.com/xzpeter/linux/tree/uffd-wp-shmem-hugetlbfs [2] https://github.com/xzpeter/umap-apps/tree/peter [3] https://github.com/xzpeter/umap/tree/peter-shmem-hugetlbfs [4] https://github.com/xzpeter/umap-apps/commit/b0c2c7b1cd9dcb6835e7c59d02ece1f6b7f1ea01 Peter Xu (26): mm/shmem: Unconditionally set pte dirty in mfill_atomic_install_pte shmem/userfaultfd: Take care of UFFDIO_COPY_MODE_WP mm: Clear vmf->pte after pte_unmap_same() returns mm/userfaultfd: Introduce special pte for unmapped file-backed mem mm/swap: Introduce the idea of special swap ptes shmem/userfaultfd: Handle uffd-wp special pte in page fault handler mm: Drop first_index/last_index in zap_details mm: Introduce zap_details.zap_flags mm: Introduce ZAP_FLAG_SKIP_SWAP shmem/userfaultfd: Persist uffd-wp bit across zapping for file-backed shmem/userfaultfd: Allow wr-protect none pte for file-backed mem shmem/userfaultfd: Allows file-back mem to be uffd wr-protected on thps shmem/userfaultfd: Handle the left-overed special swap ptes shmem/userfaultfd: Pass over uffd-wp special swap pte when fork() mm/hugetlb: Drop __unmap_hugepage_range definition from hugetlb.h mm/hugetlb: Introduce huge pte version of uffd-wp helpers hugetlb/userfaultfd: Hook page faults for uffd write protection hugetlb/userfaultfd: Take care of UFFDIO_COPY_MODE_WP hugetlb/userfaultfd: Handle UFFDIO_WRITEPROTECT mm/hugetlb: Introduce huge version of special swap pte helpers hugetlb/userfaultfd: Handle uffd-wp special pte in hugetlb pf handler hugetlb/userfaultfd: Allow wr-protect none ptes hugetlb/userfaultfd: Only drop uffd-wp special pte if required mm/pagemap: Recognize uffd-wp bit for shmem/hugetlbfs mm/userfaultfd: Enable write protection for shmem & hugetlbfs userfaultfd/selftests: Enable uffd-wp for shmem/hugetlbfs arch/arm64/kernel/mte.c | 2 +- arch/x86/include/asm/pgtable.h | 28 +++ fs/hugetlbfs/inode.c | 15 +- fs/proc/task_mmu.c | 21 +- fs/userfaultfd.c | 41 ++-- include/asm-generic/hugetlb.h | 15 ++ include/asm-generic/pgtable_uffd.h | 3 + include/linux/hugetlb.h | 30 ++- include/linux/mm.h | 44 +++- include/linux/mm_inline.h | 42 ++++ include/linux/shmem_fs.h | 4 +- include/linux/swapops.h | 39 +++- include/linux/userfaultfd_k.h | 54 +++++ include/uapi/linux/userfaultfd.h | 10 +- mm/gup.c | 2 +- mm/hmm.c | 2 +- mm/hugetlb.c | 164 ++++++++++++--- mm/khugepaged.c | 11 +- mm/madvise.c | 4 +- mm/memcontrol.c | 2 +- mm/memory.c | 244 +++++++++++++++++------ mm/migrate.c | 4 +- mm/mincore.c | 2 +- mm/mprotect.c | 63 +++++- mm/mremap.c | 2 +- mm/page_vma_mapped.c | 6 +- mm/rmap.c | 8 + mm/shmem.c | 5 +- mm/swapfile.c | 2 +- mm/userfaultfd.c | 73 +++++-- tools/testing/selftests/vm/userfaultfd.c | 9 +- 31 files changed, 763 insertions(+), 188 deletions(-) -- 2.31.1
