From: "Mike Rapoport (Microsoft)" rppt@kernel.org
Hi,
These patches allow guest_memfd to notify userspace about minor page faults using userfaultfd and let userspace to resolve these page faults using UFFDIO_CONTINUE.
To allow UFFDIO_CONTINUE outside of the core mm I added a get_shmem_folio() callback to vm_ops that allows an address space backing a VMA to return a folio that exists in it's page cache (patch 2)
In order for guest_memfd to notify userspace about page faults, there is a new VM_FAULT_UFFD_MINOR that a ->fault() handler can return to inform the page fault handler that it needs to call handle_userfault() to complete the fault (patch 3).
Patch 4 plumbs these new goodies into guest_memfd.
This series is the minimal change I've been able to come up with to allow integration of guest_memfd with uffd and while refactoring uffd and making mfill_atomic() flow more linear would have been a nice improvement, it's way out of the scope of enabling uffd with guest_memfd.
v2 changes: * rename ->get_shared_folio() to ->get_folio() * hardwire VM_FAULF_UFFD_MINOR to 0 when CONFIG_USERFAULTFD=n
v1: https://patch.msgid.link/20251123102707.559422-1-rppt@kernel.org * Introduce VM_FAULF_UFFD_MINOR to avoid exporting handle_userfault() * Simplify vma_can_mfill_atomic() * Rename get_pagecache_folio() to get_shared_folio() and use inode instead of vma as its argument
rfc: https://patch.msgid.link/20251117114631.2029447-1-rppt@kernel.org
Mike Rapoport (Microsoft) (4): userfaultfd: move vma_can_userfault out of line userfaultfd, shmem: use a VMA callback to handle UFFDIO_CONTINUE mm: introduce VM_FAULT_UFFD_MINOR fault reason guest_memfd: add support for userfaultfd minor mode
Nikita Kalyazin (1): KVM: selftests: test userfaultfd minor for guest_memfd
include/linux/mm.h | 9 ++ include/linux/mm_types.h | 10 +- include/linux/userfaultfd_k.h | 36 +----- mm/memory.c | 2 + mm/shmem.c | 20 +++- mm/userfaultfd.c | 80 +++++++++++--- .../testing/selftests/kvm/guest_memfd_test.c | 103 ++++++++++++++++++ virt/kvm/guest_memfd.c | 28 +++++ 8 files changed, 236 insertions(+), 52 deletions(-)
base-commit: 6a23ae0a96a600d1d12557add110e0bb6e32730c