linux-kernel - [PATCH 3/7] userfaultfd: shmem: introduce vma_is

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Date:	Thu,  4 Aug 2016 11:14:14 +0300
From:	Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Pavel Emelyanov <xemul@...tuozzo.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Mike Rapoport <rppt@...ux.vnet.ibm.com>
Subject: [PATCH 3/7] userfaultfd: shmem: introduce vma_is_shmem

Currently userfault relies on vma_is_anonymous and vma_is_hugetlb to ensure
compatibility of a VMA with userfault. Introduction of vma_is_shmem allows
detection if tmpfs backed VMAs, so that they may be used with userfaultfd.
Current implementation presumes usage of vma_is_shmem only by slow path
routines in userfaultfd, therefore the vma_is_shmem is not made inline to
leave the few remaining free bits in vm_flags.

Signed-off-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
---
 include/linux/mm.h | 10 ++++++++++
 mm/shmem.c         |  5 +++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1dedeb8..7a20398 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1343,6 +1343,16 @@ static inline bool vma_is_anonymous(struct vm_area_struct *vma)
 	return !vma->vm_ops;
 }
 
+#ifdef CONFIG_SHMEM
+/*
+ * The vma_is_shmem is not inline because it is used only by slow
+ * paths in userfault.
+ */
+bool vma_is_shmem(struct vm_area_struct *vma);
+#else
+static inline bool vma_is_shmem(struct vm_area_struct *vma) { return false; }
+#endif
+
 static inline int stack_guard_page_start(struct vm_area_struct *vma,
 					     unsigned long addr)
 {
diff --git a/mm/shmem.c b/mm/shmem.c
index fcf560c..881b7a0 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -194,6 +194,11 @@ static const struct inode_operations shmem_dir_inode_operations;
 static const struct inode_operations shmem_special_inode_operations;
 static const struct vm_operations_struct shmem_vm_ops;
 
+bool vma_is_shmem(struct vm_area_struct *vma)
+{
+	return vma->vm_ops == &shmem_vm_ops;
+}
+
 static LIST_HEAD(shmem_swaplist);
 static DEFINE_MUTEX(shmem_swaplist_mutex);
 
-- 
1.9.1