From: "Mike Rapoport (Microsoft)" <[email protected]> Current userfaultfd implementation works only with memory managed by core MM: anonymous, shmem and hugetlb.
First, there is no fundamental reason to limit userfaultfd support only to the core memory types and userfaults can be handled similarly to regular page faults provided a VMA owner implements appropriate callbacks. Second, historically various code paths were conditioned on vma_is_anonymous(), vma_is_shmem() and is_vm_hugetlb_page() and some of these conditions can be expressed as operations implemented by a particular memory type. Introduce vm_uffd_ops extension to vm_operations_struct that will delegate memory type specific operations to a VMA owner. Operations for anonymous memory are handled internally in userfaultfd using anon_uffd_ops that implicitly assigned to anonymous VMAs. Start with a single operation, ->can_userfault() that will verify that a VMA meets requirements for userfaultfd support at registration time. Implement that method for anonymous, shmem and hugetlb and move relevant parts of vma_can_userfault() into the new callbacks. Signed-off-by: Mike Rapoport (Microsoft) <[email protected]> --- include/linux/mm.h | 5 +++++ include/linux/userfaultfd_k.h | 6 +++++ mm/hugetlb.c | 21 ++++++++++++++++++ mm/shmem.c | 23 ++++++++++++++++++++ mm/userfaultfd.c | 41 ++++++++++++++++++++++------------- 5 files changed, 81 insertions(+), 15 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 15076261d0c2..3c2caff646c3 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -732,6 +732,8 @@ struct vm_fault { */ }; +struct vm_uffd_ops; + /* * These are the virtual MM functions - opening of an area, closing and * unmapping it (needed to keep files on disk up-to-date etc), pointer @@ -817,6 +819,9 @@ struct vm_operations_struct { struct page *(*find_normal_page)(struct vm_area_struct *vma, unsigned long addr); #endif /* CONFIG_FIND_NORMAL_PAGE */ +#ifdef CONFIG_USERFAULTFD + const struct vm_uffd_ops *uffd_ops; +#endif }; #ifdef CONFIG_NUMA_BALANCING diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index a49cf750e803..56e85ab166c7 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -80,6 +80,12 @@ struct userfaultfd_ctx { extern vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason); +/* VMA userfaultfd operations */ +struct vm_uffd_ops { + /* Checks if a VMA can support userfaultfd */ + bool (*can_userfault)(struct vm_area_struct *vma, vm_flags_t vm_flags); +}; + /* A combined operation mode + behavior flags. */ typedef unsigned int __bitwise uffd_flags_t; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 51273baec9e5..909131910c43 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4797,6 +4797,24 @@ static vm_fault_t hugetlb_vm_op_fault(struct vm_fault *vmf) return 0; } +#ifdef CONFIG_USERFAULTFD +static bool hugetlb_can_userfault(struct vm_area_struct *vma, + vm_flags_t vm_flags) +{ + /* + * If user requested uffd-wp but not enabled pte markers for + * uffd-wp, then hugetlb is not supported. + */ + if (!uffd_supports_wp_marker() && (vm_flags & VM_UFFD_WP)) + return false; + return true; +} + +static const struct vm_uffd_ops hugetlb_uffd_ops = { + .can_userfault = hugetlb_can_userfault, +}; +#endif + /* * When a new function is introduced to vm_operations_struct and added * to hugetlb_vm_ops, please consider adding the function to shm_vm_ops. @@ -4810,6 +4828,9 @@ const struct vm_operations_struct hugetlb_vm_ops = { .close = hugetlb_vm_op_close, .may_split = hugetlb_vm_op_split, .pagesize = hugetlb_vm_op_pagesize, +#ifdef CONFIG_USERFAULTFD + .uffd_ops = &hugetlb_uffd_ops, +#endif }; static pte_t make_huge_pte(struct vm_area_struct *vma, struct folio *folio, diff --git a/mm/shmem.c b/mm/shmem.c index ec6c01378e9d..9b82cda271c4 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -5290,6 +5290,23 @@ static const struct super_operations shmem_ops = { #endif }; +#ifdef CONFIG_USERFAULTFD +static bool shmem_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags) +{ + /* + * If user requested uffd-wp but not enabled pte markers for + * uffd-wp, then shmem is not supported. + */ + if (!uffd_supports_wp_marker() && (vm_flags & VM_UFFD_WP)) + return false; + return true; +} + +static const struct vm_uffd_ops shmem_uffd_ops = { + .can_userfault = shmem_can_userfault, +}; +#endif + static const struct vm_operations_struct shmem_vm_ops = { .fault = shmem_fault, .map_pages = filemap_map_pages, @@ -5297,6 +5314,9 @@ static const struct vm_operations_struct shmem_vm_ops = { .set_policy = shmem_set_policy, .get_policy = shmem_get_policy, #endif +#ifdef CONFIG_USERFAULTFD + .uffd_ops = &shmem_uffd_ops, +#endif }; static const struct vm_operations_struct shmem_anon_vm_ops = { @@ -5306,6 +5326,9 @@ static const struct vm_operations_struct shmem_anon_vm_ops = { .set_policy = shmem_set_policy, .get_policy = shmem_get_policy, #endif +#ifdef CONFIG_USERFAULTFD + .uffd_ops = &shmem_uffd_ops, +#endif }; int shmem_init_fs_context(struct fs_context *fc) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 786f0a245675..d035f5e17f07 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -34,6 +34,25 @@ struct mfill_state { pmd_t *pmd; }; +static bool anon_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags) +{ + /* anonymous memory does not support MINOR mode */ + if (vm_flags & VM_UFFD_MINOR) + return false; + return true; +} + +static const struct vm_uffd_ops anon_uffd_ops = { + .can_userfault = anon_can_userfault, +}; + +static const struct vm_uffd_ops *vma_uffd_ops(struct vm_area_struct *vma) +{ + if (vma_is_anonymous(vma)) + return &anon_uffd_ops; + return vma->vm_ops ? vma->vm_ops->uffd_ops : NULL; +} + static __always_inline bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end) { @@ -2019,13 +2038,15 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, bool wp_async) { - vm_flags &= __VM_UFFD_FLAGS; + const struct vm_uffd_ops *ops = vma_uffd_ops(vma); - if (vma->vm_flags & VM_DROPPABLE) + /* only VMAs that implement vm_uffd_ops are supported */ + if (!ops) return false; - if ((vm_flags & VM_UFFD_MINOR) && - (!is_vm_hugetlb_page(vma) && !vma_is_shmem(vma))) + vm_flags &= __VM_UFFD_FLAGS; + + if (vma->vm_flags & VM_DROPPABLE) return false; /* @@ -2035,18 +2056,8 @@ bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, if (wp_async && (vm_flags == VM_UFFD_WP)) return true; - /* - * If user requested uffd-wp but not enabled pte markers for - * uffd-wp, then shmem & hugetlbfs are not supported but only - * anonymous. - */ - if (!uffd_supports_wp_marker() && (vm_flags & VM_UFFD_WP) && - !vma_is_anonymous(vma)) - return false; - /* By default, allow any of anon|shmem|hugetlb */ - return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) || - vma_is_shmem(vma); + return ops->can_userfault(vma, vm_flags); } static void userfaultfd_set_vm_flags(struct vm_area_struct *vma, -- 2.51.0
