From: "Mike Rapoport (Microsoft)" <[email protected]> When userspace resolves a page fault in a shmem VMA with UFFDIO_CONTINUE it needs to get a folio that already exists in the pagecache backing that VMA.
Instead of using shmem_get_folio() for that, add a get_pagecache_folio() method to 'struct vm_operations_struct' that will return a folio if it exists in the VMA's pagecache at given pgoff. Implement get_pagecache_folio() method for shmem and slightly refactor userfaultfd's mfill_atomic() and mfill_atomic_pte_continue() to support this new API. Signed-off-by: Mike Rapoport (Microsoft) <[email protected]> --- include/linux/mm.h | 9 +++++++ mm/shmem.c | 20 ++++++++++++++++ mm/userfaultfd.c | 60 ++++++++++++++++++++++++++++++---------------- 3 files changed, 69 insertions(+), 20 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index d16b33bacc32..c35c1e1ac4dd 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -690,6 +690,15 @@ 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 + /* + * Called by userfault to resolve UFFDIO_CONTINUE request. + * Should return the folio found at pgoff in the VMA's pagecache if it + * exists or ERR_PTR otherwise. + */ + struct folio *(*get_pagecache_folio)(struct vm_area_struct *vma, + pgoff_t pgoff); +#endif }; #ifdef CONFIG_NUMA_BALANCING diff --git a/mm/shmem.c b/mm/shmem.c index b9081b817d28..4ac122284bff 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -3260,6 +3260,20 @@ int shmem_mfill_atomic_pte(pmd_t *dst_pmd, shmem_inode_unacct_blocks(inode, 1); return ret; } + +static struct folio *shmem_get_pagecache_folio(struct vm_area_struct *vma, + pgoff_t pgoff) +{ + struct inode *inode = file_inode(vma->vm_file); + struct folio *folio; + int err; + + err = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC); + if (err) + return ERR_PTR(err); + + return folio; +} #endif /* CONFIG_USERFAULTFD */ #ifdef CONFIG_TMPFS @@ -5292,6 +5306,9 @@ static const struct vm_operations_struct shmem_vm_ops = { .set_policy = shmem_set_policy, .get_policy = shmem_get_policy, #endif +#ifdef CONFIG_USERFAULTFD + .get_pagecache_folio = shmem_get_pagecache_folio, +#endif }; static const struct vm_operations_struct shmem_anon_vm_ops = { @@ -5301,6 +5318,9 @@ static const struct vm_operations_struct shmem_anon_vm_ops = { .set_policy = shmem_set_policy, .get_policy = shmem_get_policy, #endif +#ifdef CONFIG_USERFAULTFD + .get_pagecache_folio = shmem_get_pagecache_folio, +#endif }; int shmem_init_fs_context(struct fs_context *fc) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 8dc964389b0d..60b3183a72c0 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -382,21 +382,17 @@ static int mfill_atomic_pte_continue(pmd_t *dst_pmd, unsigned long dst_addr, uffd_flags_t flags) { - struct inode *inode = file_inode(dst_vma->vm_file); pgoff_t pgoff = linear_page_index(dst_vma, dst_addr); struct folio *folio; struct page *page; int ret; - ret = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC); + folio = dst_vma->vm_ops->get_pagecache_folio(dst_vma, pgoff); /* Our caller expects us to return -EFAULT if we failed to find folio */ - if (ret == -ENOENT) - ret = -EFAULT; - if (ret) - goto out; - if (!folio) { - ret = -EFAULT; - goto out; + if (IS_ERR_OR_NULL(folio)) { + if (PTR_ERR(folio) == -ENOENT || !folio) + return -EFAULT; + return PTR_ERR(folio); } page = folio_file_page(folio, pgoff); @@ -411,13 +407,12 @@ static int mfill_atomic_pte_continue(pmd_t *dst_pmd, goto out_release; folio_unlock(folio); - ret = 0; -out: - return ret; + return 0; + out_release: folio_unlock(folio); folio_put(folio); - goto out; + return ret; } /* Handles UFFDIO_POISON for all non-hugetlb VMAs. */ @@ -694,6 +689,22 @@ static __always_inline ssize_t mfill_atomic_pte(pmd_t *dst_pmd, return err; } +static __always_inline bool vma_can_mfill_atomic(struct vm_area_struct *vma, + uffd_flags_t flags) +{ + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) { + if (vma->vm_ops && vma->vm_ops->get_pagecache_folio) + return true; + else + return false; + } + + if (vma_is_anonymous(vma) || vma_is_shmem(vma)) + return true; + + return false; +} + static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, @@ -766,10 +777,7 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, return mfill_atomic_hugetlb(ctx, dst_vma, dst_start, src_start, len, flags); - if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma)) - goto out_unlock; - if (!vma_is_shmem(dst_vma) && - uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) + if (!vma_can_mfill_atomic(dst_vma, flags)) goto out_unlock; while (src_addr < src_start + len) { @@ -1985,9 +1993,21 @@ bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, if (vma->vm_flags & VM_DROPPABLE) return false; - if ((vm_flags & VM_UFFD_MINOR) && - (!is_vm_hugetlb_page(vma) && !vma_is_shmem(vma))) - return false; + if (vm_flags & VM_UFFD_MINOR) { + /* + * If only MINOR mode is requested and we can request an + * existing folio from VMA's page cache, allow it + */ + if (vm_flags == VM_UFFD_MINOR && vma->vm_ops && + vma->vm_ops->get_pagecache_folio) + return true; + /* + * Only hugetlb and shmem can support MINOR mode in combination + * with other modes + */ + if (!is_vm_hugetlb_page(vma) && !vma_is_shmem(vma)) + return false; + } /* * If wp async enabled, and WP is the only mode enabled, allow any -- 2.50.1
