Hi, This series implements initial write protection support for userfaultfd. Currently both shmem and hugetlbfs are not supported yet, but only anonymous memory. To be simple, either "userfaultfd-wp" or "uffd-wp" might be used in later paragraphs. The whole series can also be found at: https://github.com/xzpeter/linux/tree/uffd-wp-merged Any comment would be greatly welcomed. Thanks. Overview ==================== The uffd-wp work was initialized by Shaohua Li [1], and later continued by Andrea [2]. This series is based upon Andrea's latest userfaultfd tree, and it is a continuous works from both Shaohua and Andrea. Many of the follow up ideas come from Andrea too. Besides the old MISSING register mode of userfaultfd, the new uffd-wp support provides another alternative register mode called UFFDIO_REGISTER_MODE_WP that can be used to listen to not only missing page faults but also write protection page faults, or even they can be registered together. At the same time, the new feature also provides a new userfaultfd ioctl called UFFDIO_WRITEPROTECT which allows the userspace to write protect a range or memory or fixup write permission of faulted pages. Please refer to the document patch "userfaultfd: wp: UFFDIO_REGISTER_MODE_WP documentation update" for more information on the new interface and what it can do. The major workflow of an uffd-wp program should be: 1. Register a memory region with WP mode using UFFDIO_REGISTER_MODE_WP 2. Write protect part of the whole registered region using UFFDIO_WRITEPROTECT, passing in UFFDIO_WRITEPROTECT_MODE_WP to show that we want to write protect the range. 3. Start a working thread that modifies the protected pages, meanwhile listening to UFFD messages. 4. When a write is detected upon the protected range, page fault happens, a UFFD message will be generated and reported to the page fault handling thread 5. The page fault handler thread resolves the page fault using the new UFFDIO_WRITEPROTECT ioctl, but this time passing in !UFFDIO_WRITEPROTECT_MODE_WP instead showing that we want to recover the write permission. Before this operation, the fault handler thread can do anything it wants, e.g., dumps the page to a persistent storage. 6. The worker thread will continue running with the correctly applied write permission from step 5. Currently there are already two projects that are based on this new userfaultfd feature. QEMU Live Snapshot: The project provides a way to allow the QEMU hypervisor to take snapshot of VMs without stopping the VM [3]. LLNL umap library: The project provides a mmap-like interface and "allow to have an application specific buffer of pages cached from a large file, i.e. out-of-core execution using memory map" [4][5]. Before posting the patchset, this series was smoke tested against QEMU live snapshot and the LLNL umap library (by doing parallel quicksort using 128 sorting threads + 80 uffd servicing threads). My sincere thanks to Marty Mcfadden and Denis Plotnikov for the help along the way. Implementation ============== Patch 1-4: The whole uffd-wp requires the kernel page fault path to take more than one retries. In the previous works starting from Shaohua, a new fault flag FAULT_FLAG_ALLOW_UFFD_RETRY was introduced for this [6]. However in this series we have dropped that patch, instead the whole work is based on the recent series "[PATCH RFC v3 0/4] mm: some enhancements to the page fault mechanism" [7] which removes the assuption that VM_FAULT_RETRY can only happen once. This four patches are identital patches but picked up here. Please refer to the cover letter [7] for more information. More discussion upstream shows that this work could even benefit existing use case [8] so please help justify whether patches 1-4 can be consider to be accepted even earlier than the rest of the series. Patch 5-21: Implements the uffd-wp logic. To avoid collision with existing write protections (e.g., an private anonymous page can be write protected if it was shared between multiple processes), a new PTE bit (_PAGE_UFFD_WP) was introduced to explicitly mark a PTE as userfault write-protected. A similar bit was also used in the swap/migration entry (_PAGE_SWP_UFFD_WP) to make sure even if the pages were swapped or migrated, the uffd-wp tracking information won't be lost. When resolving a page fault, we'll do a page copy before hand if the page was COWed to make sure we won't corrupt any shared pages. Etc. Please see separated patches for more details. Patch 22: Documentation update for uffd-wp Patch 23,24: Uffd-wp selftests TODO ============= - hugetlbfs/shmem support - performance - more architectures - ... References ========== [1] https://lwn.net/Articles/666187/ [2] https://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git/log/?h=userfault [3] https://github.com/denis-plotnikov/qemu/commits/background-snapshot-kvm [4] https://github.com/LLNL/umap [5] https://llnl-umap.readthedocs.io/en/develop/ [6] https://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git/commit/?h=userfault&id=b245ecf6cf59156966f3da6e6b674f6695a5ffa5 [7] https://lkml.org/lkml/2018/11/21/370 [8] https://lkml.org/lkml/2018/12/30/64 Andrea Arcangeli (5): userfaultfd: wp: add the writeprotect API to userfaultfd ioctl userfaultfd: wp: hook userfault handler to write protection fault userfaultfd: wp: add WP pagetable tracking to x86 userfaultfd: wp: userfaultfd_pte/huge_pmd_wp() helpers userfaultfd: wp: add UFFDIO_COPY_MODE_WP Martin Cracauer (1): userfaultfd: wp: UFFDIO_REGISTER_MODE_WP documentation update Peter Xu (15): mm: gup: rename "nonblocking" to "locked" where proper mm: userfault: return VM_FAULT_RETRY on signals mm: allow VM_FAULT_RETRY for multiple times mm: gup: allow VM_FAULT_RETRY for multiple times mm: merge parameters for change_protection() userfaultfd: wp: apply _PAGE_UFFD_WP bit mm: export wp_page_copy() userfaultfd: wp: handle COW properly for uffd-wp userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork userfaultfd: wp: add pmd_swp_*uffd_wp() helpers userfaultfd: wp: support swap and page migration userfaultfd: wp: don't wake up when doing write protect khugepaged: skip collapse if uffd-wp detected userfaultfd: selftests: refactor statistics userfaultfd: selftests: add write-protect test Shaohua Li (3): userfaultfd: wp: add helper for writeprotect check userfaultfd: wp: support write protection for userfault vma range userfaultfd: wp: enabled write protection in userfaultfd API Documentation/admin-guide/mm/userfaultfd.rst | 51 +++++ arch/alpha/mm/fault.c | 4 +- arch/arc/mm/fault.c | 12 +- arch/arm/mm/fault.c | 17 +- arch/arm64/mm/fault.c | 11 +- arch/hexagon/mm/vm_fault.c | 3 +- arch/ia64/mm/fault.c | 3 +- arch/m68k/mm/fault.c | 5 +- arch/microblaze/mm/fault.c | 3 +- arch/mips/mm/fault.c | 3 +- arch/nds32/mm/fault.c | 7 +- arch/nios2/mm/fault.c | 5 +- arch/openrisc/mm/fault.c | 3 +- arch/parisc/mm/fault.c | 4 +- arch/powerpc/mm/fault.c | 9 +- arch/riscv/mm/fault.c | 9 +- arch/s390/mm/fault.c | 14 +- arch/sh/mm/fault.c | 5 +- arch/sparc/mm/fault_32.c | 4 +- arch/sparc/mm/fault_64.c | 4 +- arch/um/kernel/trap.c | 6 +- arch/unicore32/mm/fault.c | 10 +- arch/x86/Kconfig | 1 + arch/x86/include/asm/pgtable.h | 67 ++++++ arch/x86/include/asm/pgtable_64.h | 8 +- arch/x86/include/asm/pgtable_types.h | 11 +- arch/x86/mm/fault.c | 13 +- arch/xtensa/mm/fault.c | 4 +- fs/userfaultfd.c | 110 +++++---- include/asm-generic/pgtable.h | 1 + include/asm-generic/pgtable_uffd.h | 66 ++++++ include/linux/huge_mm.h | 2 +- include/linux/mm.h | 21 +- include/linux/swapops.h | 2 + include/linux/userfaultfd_k.h | 41 +++- include/trace/events/huge_memory.h | 1 + include/uapi/linux/userfaultfd.h | 28 ++- init/Kconfig | 5 + mm/gup.c | 61 ++--- mm/huge_memory.c | 28 ++- mm/hugetlb.c | 8 +- mm/khugepaged.c | 23 ++ mm/memory.c | 28 ++- mm/mempolicy.c | 2 +- mm/migrate.c | 7 + mm/mprotect.c | 99 +++++++-- mm/rmap.c | 6 + mm/userfaultfd.c | 92 +++++++- tools/testing/selftests/vm/userfaultfd.c | 222 ++++++++++++++----- 49 files changed, 898 insertions(+), 251 deletions(-) create mode 100644 include/asm-generic/pgtable_uffd.h -- 2.17.1
