mm: introduce vma_is_anonymous(vma) helper

commit b5330628546616af14ff23075fbf8d4ad91f6e25 upstream.

special_mapping_fault() is absolutely broken.  It seems it was always
wrong, but this didn't matter until vdso/vvar started to use more than
one page.

And after this change vma_is_anonymous() becomes really trivial, it
simply checks vm_ops == NULL.  However, I do think the helper makes
sense.  There are a lot of ->vm_ops != NULL checks, the helper makes the
caller's code more understandable (self-documented) and this is more
grep-friendly.

This patch (of 3):

Preparation.  Add the new simple helper, vma_is_anonymous(vma), and change
handle_pte_fault() to use it.  It will have more users.

The name is not accurate, say a hpet_mmap()'ed vma is not anonymous.
Perhaps it should be named vma_has_fault() instead.  But it matches the
logic in mmap.c/memory.c (see next changes).  "True" just means that a
page fault will use do_anonymous_page().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.16 as dependency of "mm/mincore.c: make mincore() more
 conservative"; adjusted context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

2 files changed, 9 insertions, 4 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 42a3552f641a..a576467cd4a5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1241,6 +1241,11 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen);
 
 int vma_is_stack_for_task(struct vm_area_struct *vma, struct task_struct *t);
 
+static inline bool vma_is_anonymous(struct vm_area_struct *vma)
+{
+	return !vma->vm_ops;
+}
+
 extern unsigned long move_page_tables(struct vm_area_struct *vma,
 		unsigned long old_addr, struct vm_area_struct *new_vma,
 		unsigned long new_addr, unsigned long len,
diff --git a/mm/memory.c b/mm/memory.c
index 62c2c8a148b0..1de5302d5738 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3105,12 +3105,12 @@ static int handle_pte_fault(struct mm_struct *mm,
 	entry = *pte;
 	if (!pte_present(entry)) {
 		if (pte_none(entry)) {
-			if (vma->vm_ops)
+			if (vma_is_anonymous(vma))
+				return do_anonymous_page(mm, vma, address,
+							 pte, pmd, flags);
+			else
 				return do_fault(mm, vma, address, pte,
 						pmd, flags, entry);
-
-			return do_anonymous_page(mm, vma, address,
-						 pte, pmd, flags);
 		}
 		return do_swap_page(mm, vma, address,
 					pte, pmd, flags, entry);