On Mon, Nov 24, 2025 at 12:05:18PM +0100, David Hildenbrand (Red Hat) wrote: > On 11/23/25 11:27, Mike Rapoport wrote: > > From: "Mike Rapoport (Microsoft)" <[email protected]> > > > > When a VMA is registered with userfaulfd in minor mode, its ->fault() > > method should check if a folio exists in the page cache and if yes > > ->fault() should call handle_userfault(VM_UFFD_MISSING). > > > > Instead of calling handle_userfault() directly from a specific ->fault() > > implementation introduce new fault reason VM_FAULT_UFFD_MINOR that will > > notify the core page fault handler that it should call > > handle_userfaultfd(VM_UFFD_MISSING) to complete a page fault. > > > > Replace a call to handle_userfault(VM_UFFD_MISSING) in shmem and use the > > new VM_FAULT_UFFD_MINOR there instead. > > > > Suggested-by: David Hildenbrand (Red Hat) <[email protected]> > > Signed-off-by: Mike Rapoport (Microsoft) <[email protected]> > > --- > > include/linux/mm_types.h | 3 +++ > > mm/memory.c | 2 ++ > > mm/shmem.c | 2 +- > > 3 files changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > > index 90e5790c318f..eb135369940f 100644 > > --- a/include/linux/mm_types.h > > +++ b/include/linux/mm_types.h > > @@ -1523,6 +1523,8 @@ typedef __bitwise unsigned int vm_fault_t; > > * fsync() to complete (for synchronous > > page faults > > * in DAX) > > * @VM_FAULT_COMPLETED: ->fault completed, meanwhile mmap lock > > released > > + * @VM_FAULT_UFFD_MINOR: ->fault did not modify page tables and needs > > + * handle_userfault(VM_UFFD_MINOR) to complete > > * @VM_FAULT_HINDEX_MASK: mask HINDEX value > > * > > */ > > @@ -1540,6 +1542,7 @@ enum vm_fault_reason { > > VM_FAULT_DONE_COW = (__force vm_fault_t)0x001000, > > VM_FAULT_NEEDDSYNC = (__force vm_fault_t)0x002000, > > VM_FAULT_COMPLETED = (__force vm_fault_t)0x004000, > > + VM_FAULT_UFFD_MINOR = (__force vm_fault_t)0x008000, > > VM_FAULT_HINDEX_MASK = (__force vm_fault_t)0x0f0000, > > }; > > diff --git a/mm/memory.c b/mm/memory.c > > index b59ae7ce42eb..94acbac8cefb 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -5279,6 +5279,8 @@ static vm_fault_t __do_fault(struct vm_fault *vmf) > > } > > ret = vma->vm_ops->fault(vmf); > > + if (unlikely(ret & VM_FAULT_UFFD_MINOR)) > > + return handle_userfault(vmf, VM_UFFD_MINOR); > > If we could define VM_FAULT_UFFD_MINOR to be 0 without USERFAULTFD, we could > optimize that check out completely on such configs. It will be a bit ugly, but we can :) > -- > Cheers > > David
-- Sincerely yours, Mike.
