mm/vma: correct incorrect vma.h inclusion

The only files which should be including vma.h are the implementation files
for the core VMA logic - vma.c, vma_init.c, and vma_exec.c.

This is in order to allow for userland testing of core VMA logic. In this
cases, vma_internal.h and vma.h are included, providing both the
dependencies upon which the core VMA logic requires and its declarations.

Userland testable VMA logic is achieved by having separate vma_internal.h
implementations for userland and kernel.

Callers other than the core VMA implementation should include internal.h
instead. This header does not need to include vma_internal.h as it only
contains the vma.h declarations, for which the includes already present
suffice.

Update code to reflect this, update comments to reflect the fact there are
3 VMA implementation files and document things more clearly.

While we're here, slightly improve the language of the comment describing
vma_exec.c.

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-30-2a5aa403d977@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/mmu_notifier.c

@@ -19,7 +19,7 @@
 #include <linux/sched/mm.h>
 #include <linux/slab.h>
 
-#include "vma.h"
+#include "internal.h"
 
 /* global SRCU for all MMs */
 DEFINE_STATIC_SRCU(srcu);

mm/nommu.c

@@ -41,7 +41,6 @@
 #include <asm/tlbflush.h>
 #include <asm/mmu_context.h>
 #include "internal.h"
-#include "vma.h"
 
 unsigned long highest_memmap_pfn;
 int heap_stack_gap = 0;

mm/vma.c

@@ -4,6 +4,10 @@
  * VMA-specific functions.
  */
 
+/*
+ * To allow for userland testing we place internal dependencies in
+ * vma_internal.h and external VMA API declarations in vma.h.
+ */
 #include "vma_internal.h"
 #include "vma.h"
 

mm/vma.h

@@ -2,7 +2,14 @@
 /*
  * vma.h
  *
- * Core VMA manipulation API implemented in vma.c.
+ * Core VMA manipulation API implemented in vma.c, vma_init.c and vma_exec.c.
+ *
+ * Note that, in order for VMA logic to be userland testable, this header
+ * intentionally includes no dependencies.
+ *
+ * This is specifically scoped to mm-only. Users of this functionality (other
+ * than the core VMA implementation itself) should not include this header
+ * directly, but rather include internal.h.
  */
 #ifndef __MM_VMA_H
 #define __MM_VMA_H

mm/vma_exec.c

@@ -1,10 +1,14 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
 /*
- * Functions explicitly implemented for exec functionality which however are
- * explicitly VMA-only logic.
+ * Functions provided for exec functionality which however are
+ * specifically VMA-only logic.
  */
 
+/*
+ * To allow for userland testing we place internal dependencies in
+ * vma_internal.h and external VMA API declarations in vma.h.
+ */
 #include "vma_internal.h"
 #include "vma.h"
 

mm/vma_init.c

@@ -5,6 +5,10 @@
  * between CONFIG_MMU and non-CONFIG_MMU kernel configurations.
  */
 
+/*
+ * To allow for userland testing we place internal dependencies in
+ * vma_internal.h and external VMA API declarations in vma.h.
+ */
 #include "vma_internal.h"
 #include "vma.h"
 

mm/vma_internal.h

@@ -2,8 +2,8 @@
 /*
  * vma_internal.h
  *
- * Headers required by vma.c, which can be substituted accordingly when testing
- * VMA functionality.
+ * Headers required by vma.c, vma_init.c and vma_exec.c, which can be
+ * substituted accordingly when testing VMA functionality.
  */
 
 #ifndef __MM_VMA_INTERNAL_H