mm: add vma_assert_locked() for !CONFIG_PER_VMA_LOCK

vma_assert_locked() is needed to replace mmap_assert_locked() once we
start using per-vma locks in userfaultfd operations.

In !CONFIG_PER_VMA_LOCK case when mm is locked, it implies that the given
VMA is locked.

Link: https://lkml.kernel.org/r/20240215182756.3448972-4-lokeshgidra@google.comSigned-off-by: Lokesh Gidra <lokeshgidra@google.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Tim Murray <timmurray@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -781,6 +781,11 @@ static inline struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 	return NULL;
 }
 
+static inline void vma_assert_locked(struct vm_area_struct *vma)
+{
+	mmap_assert_locked(vma->vm_mm);
+}
+
 static inline void release_fault_lock(struct vm_fault *vmf)
 {
 	mmap_read_unlock(vmf->vma->vm_mm);