From: "Mike Rapoport (Microsoft)" <[email protected]> Hi,
These patches enable support for userfaultfd in guest_memfd. They are quite different from the latest posting [1] so I'm restarting the versioning. As there was a lot of tension around the topic, this is an RFC to get some feedback and see how we can move forward. As the ground work I refactored userfaultfd handling of PTE-based memory types (anonymous and shmem) and converted them to use vm_uffd_ops for allocating a folio or getting an existing folio from the page cache. shmem also implements callbacks that add a folio to the page cache after the data passed in UFFDIO_COPY was copied and remove the folio from the page cache if page table update fails. In order for guest_memfd to notify userspace about page faults, there are new VM_FAULT_UFFD_MINOR and VM_FAULT_UFFD_MISSING that a ->fault() handler can return to inform the page fault handler that it needs to call handle_userfault() to complete the fault. Nikita helped to plumb these new goodies into guest_memfd and provided basic tests to verify that guest_memfd works with userfaultfd. I deliberately left hugetlb out, at least for the most part. hugetlb handles acquisition of VMA and more importantly establishing of parent page table entry differently than PTE-based memory types. This is a different abstraction level than what vm_uffd_ops provides and people objected to exposing such low level APIs as a part of VMA operations. Also, to enable uffd in guest_memfd refactoring of hugetlb is not needed and I prefer to delay it until the dust settles after the changes in this set. [1] https://lore.kernel.org/all/[email protected] Mike Rapoport (Microsoft) (12): userfaultfd: introduce mfill_copy_folio_locked() helper userfaultfd: introduce struct mfill_state userfaultfd: introduce mfill_get_pmd() helper. userfaultfd: introduce mfill_get_vma() and mfill_put_vma() userfaultfd: retry copying with locks dropped in mfill_atomic_pte_copy() userfaultfd: move vma_can_userfault out of line userfaultfd: introduce vm_uffd_ops userfaultfd, shmem: use a VMA callback to handle UFFDIO_CONTINUE userfaultfd: introduce vm_uffd_ops->alloc_folio() shmem, userfaultfd: implement shmem uffd operations using vm_uffd_ops userfaultfd: mfill_atomic() remove retry logic mm: introduce VM_FAULT_UFFD_MINOR fault reason Nikita Kalyazin (5): mm: introduce VM_FAULT_UFFD_MISSING fault reason KVM: guest_memfd: implement userfaultfd minor mode KVM: guest_memfd: implement userfaultfd missing mode KVM: selftests: test userfaultfd minor for guest_memfd KVM: selftests: test userfaultfd missing for guest_memfd include/linux/mm.h | 5 + include/linux/mm_types.h | 15 +- include/linux/shmem_fs.h | 14 - include/linux/userfaultfd_k.h | 74 +- mm/hugetlb.c | 21 + mm/memory.c | 8 +- mm/shmem.c | 188 +++-- mm/userfaultfd.c | 671 ++++++++++-------- .../testing/selftests/kvm/guest_memfd_test.c | 191 +++++ virt/kvm/guest_memfd.c | 134 +++- 10 files changed, 871 insertions(+), 450 deletions(-) base-commit: f8f9c1f4d0c7a64600e2ca312dec824a0bc2f1da -- 2.51.0
