mm: move vma_policy() and anon_vma_name() decls to mm_types.h

Patch series "Abstract vma_merge() and split_vma()", v4.

The vma_merge() interface is very confusing and its implementation has led
to numerous bugs as a result of that confusion.

In addition there is duplication both in invocation of vma_merge(), but
also in the common mprotect()-style pattern of attempting a merge, then if
this fails, splitting the portion of a VMA about to have its attributes
changed.

This pattern has been copy/pasted around the kernel in each instance where
such an operation has been required, each very slightly modified from the
last to make it even harder to decipher what is going on.

Simplify the whole thing by dividing the actual uses of vma_merge() and
split_vma() into specific and abstracted functions and de-duplicate the
vma_merge()/split_vma() pattern altogether.

Doing so also opens the door to changing how vma_merge() is implemented -
by knowing precisely what cases a caller is invoking rather than having a
central interface where anything might happen we can untangle the brittle
and confusing vma_merge() implementation into something more workable.

For mprotect()-like cases we introduce vma_modify() which performs the
vma_merge()/split_vma() pattern, returning a pointer to either the merged
or split VMA or an ERR_PTR(err) if the splits fail.

We provide a number of inline helper functions to make things even clearer:-

* vma_modify_flags()      - Prepare to modify the VMA's flags.
* vma_modify_flags_name() - Prepare to modify the VMA's flags/anon_vma_name
* vma_modify_policy()     - Prepare to modify the VMA's mempolicy.
* vma_modify_flags_uffd() - Prepare to modify the VMA's flags/uffd context.

For cases where a new VMA is attempted to be merged with adjacent VMAs we
add:-

* vma_merge_new_vma() - Prepare to merge a new VMA.
* vma_merge_extend()  - Prepare to extend the end of a new VMA.


This patch (of 5):

The vma_policy() define is a helper specifically for a VMA field so it
makes sense to host it in the memory management types header.

The anon_vma_name(), anon_vma_name_alloc() and anon_vma_name_free()
functions are a little out of place in mm_inline.h as they define external
functions, and so it makes sense to locate them in mm_types.h.

The purpose of these relocations is to make it possible to abstract static
inline wrappers which invoke both of these helpers.

Link: https://lkml.kernel.org/r/cover.1697043508.git.lstoakes@gmail.com
Link: https://lkml.kernel.org/r/24bfc6c9e382fffbcb0ea8d424392c27d56cc8ca.1697043508.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 36c5b43999e6..21eb56145f57 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -546,6 +546,27 @@ struct anon_vma_name {
 	char name[];
 };
 
+#ifdef CONFIG_ANON_VMA_NAME
+/*
+ * mmap_lock should be read-locked when calling anon_vma_name(). Caller should
+ * either keep holding the lock while using the returned pointer or it should
+ * raise anon_vma_name refcount before releasing the lock.
+ */
+struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma);
+struct anon_vma_name *anon_vma_name_alloc(const char *name);
+void anon_vma_name_free(struct kref *kref);
+#else /* CONFIG_ANON_VMA_NAME */
+static inline struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma)
+{
+	return NULL;
+}
+
+static inline struct anon_vma_name *anon_vma_name_alloc(const char *name)
+{
+	return NULL;
+}
+#endif
+
 struct vma_lock {
 	struct rw_semaphore lock;
 };
@@ -662,6 +683,12 @@ struct vm_area_struct {
 	struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
 } __randomize_layout;
 
+#ifdef CONFIG_NUMA
+#define vma_policy(vma) ((vma)->vm_policy)
+#else
+#define vma_policy(vma) NULL
+#endif
+
 #ifdef CONFIG_SCHED_MM_CID
 struct mm_cid {
 	u64 time;