This series is built on top of the Fuad's v7 "mapping guest_memfd backed memory at the host" [1].
With James's KVM userfault [2], it is possible to handle stage-2 faults in guest_memfd in userspace. However, KVM itself also triggers faults in guest_memfd in some cases, for example: PV interfaces like kvmclock, PV EOI and page table walking code when fetching the MMIO instruction on x86. It was agreed in the guest_memfd upstream call on 23 Jan 2025 [3] that KVM would be accessing those pages via userspace page tables. In order for such faults to be handled in userspace, guest_memfd needs to support userfaultfd. Changes since v2 [4]: - James: Fix sgp type when calling shmem_get_folio_gfp - James: Improved vm_ops->fault() error handling - James: Add and make use of the can_userfault() VMA operation - James: Add UFFD_FEATURE_MINOR_GUEST_MEMFD feature flag - James: Fix typos and add more checks in the test Nikita [1] https://lore.kernel.org/kvm/20250318161823.4005529-1-ta...@google.com/T/ [2] https://lore.kernel.org/kvm/20250109204929.1106563-1-jthough...@google.com/T/ [3] https://docs.google.com/document/d/1M6766BzdY1Lhk7LiR5IqVR8B8mG3cr-cxTxOrAosPOk/edit?tab=t.0#heading=h.w1126rgli5e3 [4] https://lore.kernel.org/kvm/20250402160721.97596-1-kalya...@amazon.com/T/ Nikita Kalyazin (6): mm: userfaultfd: generic continue for non hugetlbfs mm: provide can_userfault vma operation mm: userfaultfd: use can_userfault vma operation KVM: guest_memfd: add support for userfaultfd minor mm: userfaultfd: add UFFD_FEATURE_MINOR_GUEST_MEMFD KVM: selftests: test userfaultfd minor for guest_memfd fs/userfaultfd.c | 3 +- include/linux/mm.h | 5 + include/linux/mm_types.h | 4 + include/linux/userfaultfd_k.h | 10 +- include/uapi/linux/userfaultfd.h | 8 +- mm/hugetlb.c | 9 +- mm/shmem.c | 17 +++- mm/userfaultfd.c | 47 ++++++--- .../testing/selftests/kvm/guest_memfd_test.c | 99 +++++++++++++++++++ virt/kvm/guest_memfd.c | 10 ++ 10 files changed, 188 insertions(+), 24 deletions(-) base-commit: 3cc51efc17a2c41a480eed36b31c1773936717e0 -- 2.47.1
