mm/vma: move __install_special_mapping() to vma.c

This function is operating on VMAs and rightly belongs in vma.c, where it
can be subject to VMA userland testing and allows us to isolate it from the
rest of mm.

The _install_special_mapping() function will remain in mmap.c as a wrapper,
since this is used by architecture-specific code.

Doing so allows us to isolate more functions in vma.c for the same reasons.

This forms part of work to allow for tracking MAP_PRIVATE file-backed
mappings by their anonymous virtual page offset, as doing so allows us to
isolate and keep code that interacts with this together.

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-24-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap.c

@@ -1447,44 +1447,6 @@ static vm_fault_t special_mapping_fault(struct vm_fault *vmf)
 	return VM_FAULT_SIGBUS;
 }
 
-static struct vm_area_struct *__install_special_mapping(
-	struct mm_struct *mm,
-	unsigned long addr, unsigned long len,
-	vm_flags_t vm_flags, void *priv,
-	const struct vm_operations_struct *ops)
-{
-	int ret;
-	struct vm_area_struct *vma;
-
-	vma = vm_area_alloc(mm);
-	if (unlikely(vma == NULL))
-		return ERR_PTR(-ENOMEM);
-
-	vma_set_range(vma, addr, addr + len, 0);
-	vm_flags |= mm->def_flags | VM_DONTEXPAND;
-	if (pgtable_supports_soft_dirty())
-		vm_flags |= VM_SOFTDIRTY;
-	vm_flags_init(vma, vm_flags & ~VM_LOCKED_MASK);
-	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
-
-	vma->vm_ops = ops;
-	vma->vm_private_data = priv;
-
-	ret = insert_vm_struct(mm, vma);
-	if (ret)
-		goto out;
-
-	vm_stat_account(mm, vma->vm_flags, len >> PAGE_SHIFT);
-
-	perf_event_mmap(vma);
-
-	return vma;
-
-out:
-	vm_area_free(vma);
-	return ERR_PTR(ret);
-}
-
 bool vma_is_special_mapping(const struct vm_area_struct *vma,
 	const struct vm_special_mapping *sm)
 {

mm/vma.c

@@ -3399,3 +3399,41 @@ __weak unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
 {
 	return vma_kernel_pagesize(vma);
 }
+
+struct vm_area_struct *__install_special_mapping(
+	struct mm_struct *mm,
+	unsigned long addr, unsigned long len,
+	vm_flags_t vm_flags, void *priv,
+	const struct vm_operations_struct *ops)
+{
+	int ret;
+	struct vm_area_struct *vma;
+
+	vma = vm_area_alloc(mm);
+	if (unlikely(vma == NULL))
+		return ERR_PTR(-ENOMEM);
+
+	vma_set_range(vma, addr, addr + len, 0);
+	vm_flags |= mm->def_flags | VM_DONTEXPAND;
+	if (pgtable_supports_soft_dirty())
+		vm_flags |= VM_SOFTDIRTY;
+	vm_flags_init(vma, vm_flags & ~VM_LOCKED_MASK);
+	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
+
+	vma->vm_ops = ops;
+	vma->vm_private_data = priv;
+
+	ret = insert_vm_struct(mm, vma);
+	if (ret)
+		goto out;
+
+	vm_stat_account(mm, vma->vm_flags, len >> PAGE_SHIFT);
+
+	perf_event_mmap(vma);
+
+	return vma;
+
+out:
+	vm_area_free(vma);
+	return ERR_PTR(ret);
+}

mm/vma.h

@@ -775,4 +775,9 @@ static inline bool map_deny_write_exec(const vma_flags_t *old,
 }
 #endif
 
+struct vm_area_struct *__install_special_mapping(struct mm_struct *mm,
+		unsigned long addr, unsigned long len,
+		vm_flags_t vm_flags, void *priv,
+		const struct vm_operations_struct *ops);
+
 #endif	/* __MM_VMA_H */