From: "Mike Rapoport (Microsoft)" rppt@kernel.org
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) rppt@kernel.org --- include/linux/mm.h | 9 ++++++++ mm/shmem.c | 19 +++++++++++++++++ mm/userfaultfd.c | 52 +++++++++++++++++++++++++++++----------------- 3 files changed, 61 insertions(+), 19 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h index 7c79b3369b82..a5747c306cc2 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. + * The returned folio is locked and with reference held. + */ + struct folio *(*get_shared_folio)(struct inode *inode, pgoff_t pgoff); +#endif };
#ifdef CONFIG_NUMA_BALANCING diff --git a/mm/shmem.c b/mm/shmem.c index 58701d14dd96..aaa21bb60f51 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -3263,6 +3263,19 @@ int shmem_mfill_atomic_pte(pmd_t *dst_pmd, shmem_inode_unacct_blocks(inode, 1); return ret; } + +static struct folio *shmem_get_shared_folio(struct inode *inode, + pgoff_t pgoff) +{ + 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 @@ -5295,6 +5308,9 @@ static const struct vm_operations_struct shmem_vm_ops = { .set_policy = shmem_set_policy, .get_policy = shmem_get_policy, #endif +#ifdef CONFIG_USERFAULTFD + .get_shared_folio = shmem_get_shared_folio, +#endif };
static const struct vm_operations_struct shmem_anon_vm_ops = { @@ -5304,6 +5320,9 @@ 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_shared_folio = shmem_get_shared_folio, +#endif };
int shmem_init_fs_context(struct fs_context *fc) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 8dc964389b0d..04563f88aab5 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -388,15 +388,12 @@ static int mfill_atomic_pte_continue(pmd_t *dst_pmd, struct page *page; int ret;
- ret = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC); + folio = dst_vma->vm_ops->get_shared_folio(inode, 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 +408,12 @@ 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 +690,15 @@ 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)) + return vma->vm_ops && vma->vm_ops->get_shared_folio; + + return vma_is_anonymous(vma) || vma_is_shmem(vma); +} + static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, @@ -766,10 +771,7 @@ 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 +1987,21 @@ 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_shared_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