mm: rename walk_page_range_mm()

Patch series "mm: perform guard region install/remove under VMA lock", v2.

There is no reason why can't perform guard region operations under the VMA
lock, as long we take proper precautions to ensure that we do so in a safe
manner.

This is fine, as VMA lock acquisition is always best-effort, so if we are
unable to do so, we can simply fall back to using the mmap read lock.

Doing so will reduce mmap lock contention for callers performing guard
region operations and help establish a precedent of trying to use the VMA
lock where possible.

As part of this change we perform a trivial rename of page walk functions
which bypass safety checks (i.e. whether or not mm_walk_ops->install_pte
is specified) in order that we can keep naming consistent with the mm
walk.

This is because we need to expose a VMA-specific walk that still allows us
to install PTE entries.


This patch (of 2):

Make it clear we're referencing an unsafe variant of this function
explicitly.

This is laying the foundation for exposing more such functions and
maintaining a consistent naming scheme.

As a part of this change, rename check_ops_valid() to check_ops_safe() for
consistency.

Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/c684d91[e-mail]
Signed-off-by: Lorenzo Stoakes <[e-mail]>
Acked-by: David Hildenbrand (Red Hat) <[e-mail]>
Reviewed-by: Davidlohr Bueso <[e-mail]>
Reviewed-by: Vlastimil Babka <[e-mail]>
Acked-by: SeongJae Park <[e-mail]>
Cc: Jann Horn <[e-mail]>
Cc: Liam Howlett <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Suren Baghdasaryan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/internal.h

···
 #endif /* CONFIG_UNACCEPTED_MEMORY */
 
 /* pagewalk.c */
-int walk_page_range_mm(struct mm_struct *mm, unsigned long start,
+int walk_page_range_mm_unsafe(struct mm_struct *mm, unsigned long start,
 		unsigned long end, const struct mm_walk_ops *ops,
 		void *private);
 int walk_page_range_debug(struct mm_struct *mm, unsigned long start,

mm/madvise.c

···
 		unsigned long nr_pages = 0;
 
 		/* Returns < 0 on error, == 0 if success, > 0 if zap needed. */
-		err = walk_page_range_mm(vma->vm_mm, range->start, range->end,
-					 &guard_install_walk_ops, &nr_pages);
+		err = walk_page_range_mm_unsafe(vma->vm_mm, range->start,
+				range->end, &guard_install_walk_ops, &nr_pages);
 		if (err < 0)
 			return err;
 

mm/pagewalk.c

···
  * We usually restrict the ability to install PTEs, but this functionality is
  * available to internal memory management code and provided in mm/internal.h.
  */
-int walk_page_range_mm(struct mm_struct *mm, unsigned long start,
+int walk_page_range_mm_unsafe(struct mm_struct *mm, unsigned long start,
 		unsigned long end, const struct mm_walk_ops *ops,
 		void *private)
 {
···
  * This check is performed on all functions which are parameterised by walk
  * operations and exposed in include/linux/pagewalk.h.
  *
- * Internal memory management code can use the walk_page_range_mm() function to
- * be able to use all page walking operations.
+ * Internal memory management code can use *_unsafe() functions to be able to
+ * use all page walking operations.
  */
-static bool check_ops_valid(const struct mm_walk_ops *ops)
+static bool check_ops_safe(const struct mm_walk_ops *ops)
 {
 	/*
 	 * The installation of PTEs is solely under the control of memory
···
 		unsigned long end, const struct mm_walk_ops *ops,
 		void *private)
 {
-	if (!check_ops_valid(ops))
+	if (!check_ops_safe(ops))
 		return -EINVAL;
 
-	return walk_page_range_mm(mm, start, end, ops, private);
+	return walk_page_range_mm_unsafe(mm, start, end, ops, private);
 }
 
 /**
···
 
 	if (start >= end)
 		return -EINVAL;
-	if (!check_ops_valid(ops))
+	if (!check_ops_safe(ops))
 		return -EINVAL;
 
 	return walk_pgd_range(start, end, &walk);
···
 						    pgd, private);
 	if (start >= end || !walk.mm)
 		return -EINVAL;
-	if (!check_ops_valid(ops))
+	if (!check_ops_safe(ops))
 		return -EINVAL;
 
 	/*
···
 		return -EINVAL;
 	if (start < vma->vm_start || end > vma->vm_end)
 		return -EINVAL;
-	if (!check_ops_valid(ops))
+	if (!check_ops_safe(ops))
 		return -EINVAL;
 
 	process_mm_walk_lock(walk.mm, ops->walk_lock);
···
 
 	if (!walk.mm)
 		return -EINVAL;
-	if (!check_ops_valid(ops))
+	if (!check_ops_safe(ops))
 		return -EINVAL;
 
 	process_mm_walk_lock(walk.mm, ops->walk_lock);
···
 	unsigned long start_addr, end_addr;
 	int err = 0;
 
-	if (!check_ops_valid(ops))
+	if (!check_ops_safe(ops))
 		return -EINVAL;
 
 	lockdep_assert_held(&mapping->i_mmap_rwsem);