Previously, when a driver needed to do something like establish a reference count, it could do so in the mmap hook in the knowledge that the mapping would succeed.
With the introduction of f_op->mmap_prepare this is no longer the case, as it is invoked prior to actually establishing the mapping. To take this into account, introduce a new vm_ops->mapped callback which is invoked when the VMA is first mapped (though notably - not when it is merged - which is correct and mirrors existing mmap/open/close behaviour). We do better that vm_ops->open() here, as this callback can return an error, at which point the VMA will be unmapped. Note that vm_ops->mapped() is invoked after any mmap action is complete (such as I/O remapping). We intentionally do not expose the VMA at this point, exposing only the fields that could be used, and an output parameter in case the operation needs to update the vma->vm_private_data field. In order to deal with stacked filesystems which invoke inner filesystem's mmap() invocations, add __compat_vma_mapped() and invoke it on vfs_mmap() (via compat_vma_mmap()) to ensure that the mapped callback is handled when an mmap() caller invokes a nested filesystem's mmap_prepare() callback. We can now also remove call_action_complete() and invoke mmap_action_complete() directly, as we separate out the rmap lock logic to be called in __mmap_region() instead via maybe_drop_file_rmap_lock(). We also abstract unmapping of a VMA on mmap action completion into its own helper function, unmap_vma_locked(). Additionally, update VMA userland test headers to reflect the change. Signed-off-by: Lorenzo Stoakes (Oracle) <[email protected]> --- include/linux/fs.h | 9 +++- include/linux/mm.h | 17 +++++++ mm/internal.h | 10 ++++ mm/util.c | 86 ++++++++++++++++++++++++--------- mm/vma.c | 41 +++++++++++----- tools/testing/vma/include/dup.h | 34 ++++++++++++- 6 files changed, 158 insertions(+), 39 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index a2628a12bd2b..c390f5c667e3 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2059,13 +2059,20 @@ static inline bool can_mmap_file(struct file *file) } int compat_vma_mmap(struct file *file, struct vm_area_struct *vma); +int __vma_check_mmap_hook(struct vm_area_struct *vma); static inline int vfs_mmap(struct file *file, struct vm_area_struct *vma) { + int err; + if (file->f_op->mmap_prepare) return compat_vma_mmap(file, vma); - return file->f_op->mmap(file, vma); + err = file->f_op->mmap(file, vma); + if (err) + return err; + + return __vma_check_mmap_hook(vma); } static inline int vfs_mmap_prepare(struct file *file, struct vm_area_desc *desc) diff --git a/include/linux/mm.h b/include/linux/mm.h index 12a0b4c63736..7333d5db1221 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -759,6 +759,23 @@ struct vm_operations_struct { * Context: User context. May sleep. Caller holds mmap_lock. */ void (*close)(struct vm_area_struct *vma); + /** + * @mapped: Called when the VMA is first mapped in the MM. Not called if + * the new VMA is merged with an adjacent VMA. + * + * The @vm_private_data field is an output field allowing the user to + * modify vma->vm_private_data as necessary. + * + * ONLY valid if set from f_op->mmap_prepare. Will result in an error if + * set from f_op->mmap. + * + * Returns %0 on success, or an error otherwise. On error, the VMA will + * be unmapped. + * + * Context: User context. May sleep. Caller holds mmap_lock. + */ + int (*mapped)(unsigned long start, unsigned long end, pgoff_t pgoff, + const struct file *file, void **vm_private_data); /* Called any time before splitting to check if it's allowed */ int (*may_split)(struct vm_area_struct *vma, unsigned long addr); int (*mremap)(struct vm_area_struct *vma); diff --git a/mm/internal.h b/mm/internal.h index 7bfa85b5e78b..f0f2cf1caa36 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -158,6 +158,8 @@ static inline void *folio_raw_mapping(const struct folio *folio) * mmap hook and safely handle error conditions. On error, VMA hooks will be * mutated. * + * IMPORTANT: f_op->mmap() is deprecated, prefer f_op->mmap_prepare(). + * * @file: File which backs the mapping. * @vma: VMA which we are mapping. * @@ -201,6 +203,14 @@ static inline void vma_close(struct vm_area_struct *vma) /* unmap_vmas is in mm/memory.c */ void unmap_vmas(struct mmu_gather *tlb, struct unmap_desc *unmap); +static inline void unmap_vma_locked(struct vm_area_struct *vma) +{ + const size_t len = vma_pages(vma) << PAGE_SHIFT; + + mmap_assert_locked(vma->vm_mm); + do_munmap(vma->vm_mm, vma->vm_start, len, NULL); +} + #ifdef CONFIG_MMU static inline void get_anon_vma(struct anon_vma *anon_vma) diff --git a/mm/util.c b/mm/util.c index dba1191725b6..2b0ed54008d6 100644 --- a/mm/util.c +++ b/mm/util.c @@ -1163,6 +1163,55 @@ void flush_dcache_folio(struct folio *folio) EXPORT_SYMBOL(flush_dcache_folio); #endif +static int __compat_vma_mmap(struct file *file, struct vm_area_struct *vma) +{ + struct vm_area_desc desc = { + .mm = vma->vm_mm, + .file = file, + .start = vma->vm_start, + .end = vma->vm_end, + + .pgoff = vma->vm_pgoff, + .vm_file = vma->vm_file, + .vma_flags = vma->flags, + .page_prot = vma->vm_page_prot, + + .action.type = MMAP_NOTHING, /* Default */ + }; + int err; + + err = vfs_mmap_prepare(file, &desc); + if (err) + return err; + + err = mmap_action_prepare(&desc, &desc.action); + if (err) + return err; + + set_vma_from_desc(vma, &desc); + return mmap_action_complete(vma, &desc.action); +} + +static int __compat_vma_mapped(struct file *file, struct vm_area_struct *vma) +{ + const struct vm_operations_struct *vm_ops = vma->vm_ops; + void *vm_private_data = vma->vm_private_data; + int err; + + if (!vm_ops->mapped) + return 0; + + err = vm_ops->mapped(vma->vm_start, vma->vm_end, vma->vm_pgoff, file, + &vm_private_data); + if (err) + unmap_vma_locked(vma); + /* Update private data if changed. */ + if (vm_private_data != vma->vm_private_data) + vma->vm_private_data = vm_private_data; + + return err; +} + /** * compat_vma_mmap() - Apply the file's .mmap_prepare() hook to an * existing VMA and execute any requested actions. @@ -1191,34 +1240,26 @@ EXPORT_SYMBOL(flush_dcache_folio); */ int compat_vma_mmap(struct file *file, struct vm_area_struct *vma) { - struct vm_area_desc desc = { - .mm = vma->vm_mm, - .file = file, - .start = vma->vm_start, - .end = vma->vm_end, - - .pgoff = vma->vm_pgoff, - .vm_file = vma->vm_file, - .vma_flags = vma->flags, - .page_prot = vma->vm_page_prot, - - .action.type = MMAP_NOTHING, /* Default */ - }; int err; - err = vfs_mmap_prepare(file, &desc); - if (err) - return err; - - err = mmap_action_prepare(&desc, &desc.action); + err = __compat_vma_mmap(file, vma); if (err) return err; - set_vma_from_desc(vma, &desc); - return mmap_action_complete(vma, &desc.action); + return __compat_vma_mapped(file, vma); } EXPORT_SYMBOL(compat_vma_mmap); +int __vma_check_mmap_hook(struct vm_area_struct *vma) +{ + /* vm_ops->mapped is not valid if mmap() is specified. */ + if (WARN_ON_ONCE(vma->vm_ops->mapped)) + return -EINVAL; + + return 0; +} +EXPORT_SYMBOL(__vma_check_mmap_hook); + static void set_ps_flags(struct page_snapshot *ps, const struct folio *folio, const struct page *page) { @@ -1316,10 +1357,7 @@ static int mmap_action_finish(struct vm_area_struct *vma, * invoked if we do NOT merge, so we only clean up the VMA we created. */ if (err) { - const size_t len = vma_pages(vma) << PAGE_SHIFT; - - do_munmap(current->mm, vma->vm_start, len, NULL); - + unmap_vma_locked(vma); if (action->error_hook) { /* We may want to filter the error. */ err = action->error_hook(err); diff --git a/mm/vma.c b/mm/vma.c index 054cf1d262fb..ef9f5a5365d1 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -2705,21 +2705,35 @@ static bool can_set_ksm_flags_early(struct mmap_state *map) return false; } -static int call_action_complete(struct mmap_state *map, - struct mmap_action *action, - struct vm_area_struct *vma) +static int call_mapped_hook(struct vm_area_struct *vma) { - int ret; + const struct vm_operations_struct *vm_ops = vma->vm_ops; + void *vm_private_data = vma->vm_private_data; + int err; - ret = mmap_action_complete(vma, action); + if (!vm_ops || !vm_ops->mapped) + return 0; + err = vm_ops->mapped(vma->vm_start, vma->vm_end, vma->vm_pgoff, + vma->vm_file, &vm_private_data); + if (err) { + unmap_vma_locked(vma); + return err; + } + /* Update private data if changed. */ + if (vm_private_data != vma->vm_private_data) + vma->vm_private_data = vm_private_data; + return 0; +} - /* If we held the file rmap we need to release it. */ - if (map->hold_file_rmap_lock) { - struct file *file = vma->vm_file; +static void maybe_drop_file_rmap_lock(struct mmap_state *map, + struct vm_area_struct *vma) +{ + struct file *file; - i_mmap_unlock_write(file->f_mapping); - } - return ret; + if (!map->hold_file_rmap_lock) + return; + file = vma->vm_file; + i_mmap_unlock_write(file->f_mapping); } static unsigned long __mmap_region(struct file *file, unsigned long addr, @@ -2773,8 +2787,11 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr, __mmap_complete(&map, vma); if (have_mmap_prepare && allocated_new) { - error = call_action_complete(&map, &desc.action, vma); + error = mmap_action_complete(vma, &desc.action); + if (!error) + error = call_mapped_hook(vma); + maybe_drop_file_rmap_lock(&map, vma); if (error) return error; } diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h index 908beb263307..47d8db809f31 100644 --- a/tools/testing/vma/include/dup.h +++ b/tools/testing/vma/include/dup.h @@ -606,12 +606,34 @@ struct vm_area_struct { } __randomize_layout; struct vm_operations_struct { - void (*open)(struct vm_area_struct * area); + /** + * @open: Called when a VMA is remapped or split. Not called upon first + * mapping a VMA. + * Context: User context. May sleep. Caller holds mmap_lock. + */ + void (*open)(struct vm_area_struct *vma); /** * @close: Called when the VMA is being removed from the MM. * Context: User context. May sleep. Caller holds mmap_lock. */ - void (*close)(struct vm_area_struct * area); + void (*close)(struct vm_area_struct *vma); + /** + * @mapped: Called when the VMA is first mapped in the MM. Not called if + * the new VMA is merged with an adjacent VMA. + * + * The @vm_private_data field is an output field allowing the user to + * modify vma->vm_private_data as necessary. + * + * ONLY valid if set from f_op->mmap_prepare. Will result in an error if + * set from f_op->mmap. + * + * Returns %0 on success, or an error otherwise. On error, the VMA will + * be unmapped. + * + * Context: User context. May sleep. Caller holds mmap_lock. + */ + int (*mapped)(unsigned long start, unsigned long end, pgoff_t pgoff, + const struct file *file, void **vm_private_data); /* Called any time before splitting to check if it's allowed */ int (*may_split)(struct vm_area_struct *area, unsigned long addr); int (*mremap)(struct vm_area_struct *area); @@ -1345,3 +1367,11 @@ static inline void vma_set_file(struct vm_area_struct *vma, struct file *file) swap(vma->vm_file, file); fput(file); } + +static inline void unmap_vma_locked(struct vm_area_struct *vma) +{ + const size_t len = vma_pages(vma) << PAGE_SHIFT; + + mmap_assert_locked(vma->vm_mm); + do_munmap(vma->vm_mm, vma->vm_start, len, NULL); +} -- 2.53.0
