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X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: * Peter Xu [250926 17:17]: > [based on latest akpm/mm-new of Sep 26th, commit e612c80ae0aeb] > > v3 changelog: > - Fixed checkpatch issues on spaces or typedef > - Dropped uffd_copy() API > - Refined commit messages here and there to reflect the removal of uffd_copy() > > v1: https://lore.kernel.org/r/20250620190342.1780170-1-peterx@redhat.com > v2: https://lore.kernel.org/r/20250627154655.2085903-1-peterx@redhat.com > > This series is an alternative proposal of what Nikita proposed here on the > initial three patches: > > https://lore.kernel.org/r/20250404154352.23078-1-kalyazin@amazon.com > > This is not yet relevant to any guest-memfd support, but paving way for it. It would be much easier to review this with the guest-memfd support in this patch set. Any chance of including the target user? > Here, the major goal is to make kernel modules be able to opt-in with any > form of userfaultfd supports, like guest-memfd. This alternative option > should hopefully be cleaner, and avoid leaking userfault details into > vm_ops.fault(). > > It also means this series does not depend on anything. It's a pure > refactoring of userfaultfd internals to provide a generic API, so that > other types of files, especially RAM based, can support userfaultfd without > touching mm/ at all. > > To achieve it, this series introduced a file operation called vm_uffd_ops. > The ops needs to be provided when a file type supports any of userfaultfd. > > With that, I moved both hugetlbfs and shmem over, whenever possible. So > far due to concerns on exposing an uffd_copy() API, the MISSING faults are > still separately processed and can only be done within mm/. Hugetlbfs kept > its special paths untouched. > > An example of shmem uffd_ops: > > static const vm_uffd_ops shmem_uffd_ops = { > .uffd_features = __VM_UFFD_FLAGS, > .uffd_ioctls = BIT(_UFFDIO_COPY) | > BIT(_UFFDIO_ZEROPAGE) | > BIT(_UFFDIO_WRITEPROTECT) | > BIT(_UFFDIO_CONTINUE) | > BIT(_UFFDIO_POISON), > .uffd_get_folio = shmem_uffd_get_folio, > }; > > No functional change expected at all after the whole series applied. There > might be some slightly stricter check on uffd ops here and there in the > last patch, but that really shouldn't stand out anywhere to anyone. > > For testing: besides the cross-compilation tests, I did also try with > uffd-stress in a VM to measure any perf difference before/after the change; > The static call becomes a pointer now. I really cannot measure anything > different, which is more or less expected. > > Comments welcomed, thanks. > > Peter Xu (4): > mm: Introduce vm_uffd_ops API > mm/shmem: Support vm_uffd_ops API > mm/hugetlb: Support vm_uffd_ops API > mm: Apply vm_uffd_ops API to core mm > > include/linux/mm.h | 9 +++ > include/linux/userfaultfd_k.h | 83 ++++++++++++++++----------- > mm/hugetlb.c | 19 +++++++ > mm/shmem.c | 25 +++++++++ > mm/userfaultfd.c | 102 ++++++++++++++++++++++++++-------- > 5 files changed, 181 insertions(+), 57 deletions(-) > > -- > 2.50.1 >