[PATCH 4/6] mm: reintroduce vma_flags_test() as a singular flag test

["Lorenzo Stoakes (Oracle)" <ljs@kernel.org>]

Since we've now renamed vma_flags_test() to vma_flags_test_any() to be very
clear as to what we are in fact testing, we now have the opportunity to
bring vma_flags_test() back, but for explicitly testing a single VMA flag.

This is useful, as often flag tests are against a single flag, and
vma_flags_test_any(flags, VMA_READ_BIT) reads oddly and potentially causes
confusion.

We use sparse to enforce that users won't accidentally pass vm_flags_t to
this function without it being flagged so this should make it harder to get
this wrong.

Of course, passing vma_flags_t to the function is impossible, as it is a
struct.

Also update the VMA tests to reflect this change.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 include/linux/mm.h              | 17 +++++++++++++++--
 mm/hugetlb.c                    |  2 +-
 mm/shmem.c                      |  4 ++--
 tools/testing/vma/include/dup.h |  8 ++++++++
 4 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 66b90de30bf6..5622d04c9ba9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1051,6 +1051,19 @@ static __always_inline vma_flags_t __mk_vma_flags(size_t count,
 	return flags;
 }
 
+/*
+ * Test whether a specific VMA flag is set, e.g.:
+ *
+ * if (vma_flags_test(flags, VMA_READ_BIT)) { ... }
+ */
+static __always_inline bool vma_flags_test(const vma_flags_t *flags,
+		vma_flag_t bit)
+{
+	const unsigned long *bitmap = flags->__vma_flags;
+
+	return test_bit((__force int)bit, bitmap);
+}
+
 /*
  * Helper macro which bitwise-or combines the specified input flags into a
  * vma_flags_t bitmap value. E.g.:
@@ -1957,8 +1970,8 @@ static inline bool vma_desc_is_cow_mapping(struct vm_area_desc *desc)
 {
 	const vma_flags_t *flags = &desc->vma_flags;
 
-	return vma_flags_test_any(flags, VMA_MAYWRITE_BIT) &&
-		!vma_flags_test_any(flags, VMA_SHARED_BIT);
+	return vma_flags_test(flags, VMA_MAYWRITE_BIT) &&
+		!vma_flags_test(flags, VMA_SHARED_BIT);
 }
 
 #ifndef CONFIG_MMU
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8286c5db2c12..bd9f3b2d2cb0 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6591,7 +6591,7 @@ long hugetlb_reserve_pages(struct inode *inode,
 	 * attempt will be made for VM_NORESERVE to allocate a page
 	 * without using reserves
 	 */
-	if (vma_flags_test_any(&vma_flags, VMA_NORESERVE_BIT))
+	if (vma_flags_test(&vma_flags, VMA_NORESERVE_BIT))
 		return 0;
 
 	/*
diff --git a/mm/shmem.c b/mm/shmem.c
index 965a8908200b..5e7dcf5bc5d3 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3086,7 +3086,7 @@ static struct inode *__shmem_get_inode(struct mnt_idmap *idmap,
 	spin_lock_init(&info->lock);
 	atomic_set(&info->stop_eviction, 0);
 	info->seals = F_SEAL_SEAL;
-	info->flags = vma_flags_test_any(&flags, VMA_NORESERVE_BIT)
+	info->flags = vma_flags_test(&flags, VMA_NORESERVE_BIT)
 		? SHMEM_F_NORESERVE : 0;
 	info->i_crtime = inode_get_mtime(inode);
 	info->fsflags = (dir == NULL) ? 0 :
@@ -5827,7 +5827,7 @@ static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name,
 				       unsigned int i_flags)
 {
 	const unsigned long shmem_flags =
-		vma_flags_test_any(&flags, VMA_NORESERVE_BIT) ? SHMEM_F_NORESERVE : 0;
+		vma_flags_test(&flags, VMA_NORESERVE_BIT) ? SHMEM_F_NORESERVE : 0;
 	struct inode *inode;
 	struct file *res;
 
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index ef6b9d963acc..630478f0d583 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -844,6 +844,14 @@ static inline vma_flags_t __mk_vma_flags(size_t count, const vma_flag_t *bits);
 #define mk_vma_flags(...) __mk_vma_flags(COUNT_ARGS(__VA_ARGS__), \
 					 (const vma_flag_t []){__VA_ARGS__})
 
+static __always_inline bool vma_flags_test(const vma_flags_t *flags,
+		vma_flag_t bit)
+{
+	const unsigned long *bitmap = flags->__vma_flags;
+
+	return test_bit((__force int)bit, bitmap);
+}
+
 static __always_inline bool vma_flags_test_any_mask(const vma_flags_t *flags,
 		vma_flags_t to_test)
 {
-- 
2.53.0