[PATCH v4 15/25] mm: introduce vma_flags_count() and vma[_flags]_test_single_mask()

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

vma_flags_count() determines how many bits are set in VMA flags, using
bitmap_weight().

vma_flags_test_single_mask() determines if a vma_flags_t set of flags
contains a single flag specified as another vma_flags_t value, or if the
sought flag mask is empty, it is defined to return false.

This is useful when we want to declare a VMA flag as optionally a single
flag in a mask or empty depending on kernel configuration.

This allows us to have VM_NONE-like semantics when checking whether the
flag is set.

In a subsequent patch, we introduce the use of VMA_DROPPABLE of type
vma_flags_t using precisely these semantics.

It would be actively confusing to use vma_flags_test_any_single_mask() for
this (and vma_flags_test_all_mask() is not correct to use here, as it
trivially returns true when tested against an empty vma flags mask).

We introduce vma_flags_count() to be able to assert that the compared flag
mask is singular or empty, checked when CONFIG_DEBUG_VM is enabled.

Also update the VMA tests as part of this change.

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 include/linux/mm.h                 | 46 ++++++++++++++++++++++++++++++
 tools/testing/vma/include/custom.h |  6 ----
 tools/testing/vma/include/dup.h    | 21 ++++++++++++++
 tools/testing/vma/vma_internal.h   |  6 ++++
 4 files changed, 73 insertions(+), 6 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 47bf9f166924..324b6e8a66fa 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1083,6 +1083,14 @@ static __always_inline vma_flags_t __mk_vma_flags(vma_flags_t flags,
 #define append_vma_flags(flags, ...) __mk_vma_flags(flags,			\
 		COUNT_ARGS(__VA_ARGS__), (const vma_flag_t []){__VA_ARGS__})
 
+/* Calculates the number of set bits in the specified VMA flags. */
+static __always_inline int vma_flags_count(const vma_flags_t *flags)
+{
+	const unsigned long *bitmap = flags->__vma_flags;
+
+	return bitmap_weight(bitmap, NUM_VMA_FLAG_BITS);
+}
+
 /*
  * Test whether a specific VMA flag is set, e.g.:
  *
@@ -1158,6 +1166,26 @@ static __always_inline bool vma_flags_test_all_mask(const vma_flags_t *flags,
 #define vma_flags_test_all(flags, ...) \
 	vma_flags_test_all_mask(flags, mk_vma_flags(__VA_ARGS__))
 
+/*
+ * Helper to test that a flag mask of type vma_flags_t has a SINGLE flag set
+ * (returning false if flagmask has no flags set).
+ *
+ * This is defined to make the semantics clearer when testing an optionally
+ * defined VMA flags mask, e.g.:
+ *
+ * if (vma_flags_test_single_mask(&flags, VMA_DROPPABLE)) { ... }
+ *
+ * When VMA_DROPPABLE is defined if available, or set to EMPTY_VMA_FLAGS
+ * otherwise.
+ */
+static __always_inline bool vma_flags_test_single_mask(const vma_flags_t *flags,
+		vma_flags_t flagmask)
+{
+	VM_WARN_ON_ONCE(vma_flags_count(&flagmask) > 1);
+
+	return vma_flags_test_any_mask(flags, flagmask);
+}
+
 /* Set each of the to_set flags in flags, non-atomically. */
 static __always_inline void vma_flags_set_mask(vma_flags_t *flags,
 		vma_flags_t to_set)
@@ -1286,6 +1314,24 @@ static __always_inline bool vma_test_all_mask(const struct vm_area_struct *vma,
 #define vma_test_all(vma, ...) \
 	vma_test_all_mask(vma, mk_vma_flags(__VA_ARGS__))
 
+/*
+ * Helper to test that a flag mask of type vma_flags_t has a SINGLE flag set
+ * (returning false if flagmask has no flags set).
+ *
+ * This is useful when a flag needs to be either defined or not depending upon
+ * kernel configuration, e.g.:
+ *
+ * if (vma_test_single_mask(vma, VMA_DROPPABLE)) { ... }
+ *
+ * When VMA_DROPPABLE is defined if available, or set to EMPTY_VMA_FLAGS
+ * otherwise.
+ */
+static __always_inline bool
+vma_test_single_mask(const struct vm_area_struct *vma, vma_flags_t flagmask)
+{
+	return vma_flags_test_single_mask(&vma->flags, flagmask);
+}
+
 /*
  * Helper to set all VMA flags in a VMA.
  *
diff --git a/tools/testing/vma/include/custom.h b/tools/testing/vma/include/custom.h
index 2c498e713fbd..b7d9eb0a44e4 100644
--- a/tools/testing/vma/include/custom.h
+++ b/tools/testing/vma/include/custom.h
@@ -15,12 +15,6 @@ extern unsigned long dac_mmap_min_addr;
 #define dac_mmap_min_addr	0UL
 #endif
 
-#define VM_WARN_ON(_expr) (WARN_ON(_expr))
-#define VM_WARN_ON_ONCE(_expr) (WARN_ON_ONCE(_expr))
-#define VM_WARN_ON_VMG(_expr, _vmg) (WARN_ON(_expr))
-#define VM_BUG_ON(_expr) (BUG_ON(_expr))
-#define VM_BUG_ON_VMA(_expr, _vma) (BUG_ON(_expr))
-
 #define TASK_SIZE ((1ul << 47)-PAGE_SIZE)
 
 /*
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index f9fe07a8a443..244ee02dc21d 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -905,6 +905,13 @@ static __always_inline vma_flags_t __mk_vma_flags(vma_flags_t flags,
 #define append_vma_flags(flags, ...) __mk_vma_flags(flags,			\
 		COUNT_ARGS(__VA_ARGS__), (const vma_flag_t []){__VA_ARGS__})
 
+static __always_inline int vma_flags_count(const vma_flags_t *flags)
+{
+	const unsigned long *bitmap = flags->__vma_flags;
+
+	return bitmap_weight(bitmap, NUM_VMA_FLAG_BITS);
+}
+
 static __always_inline bool vma_flags_test(const vma_flags_t *flags,
 		vma_flag_t bit)
 {
@@ -952,6 +959,14 @@ static __always_inline bool vma_flags_test_all_mask(const vma_flags_t *flags,
 #define vma_flags_test_all(flags, ...) \
 	vma_flags_test_all_mask(flags, mk_vma_flags(__VA_ARGS__))
 
+static __always_inline bool vma_flags_test_single_mask(const vma_flags_t *flags,
+						vma_flags_t flagmask)
+{
+	VM_WARN_ON_ONCE(vma_flags_count(&flagmask) > 1);
+
+	return vma_flags_test_any_mask(flags, flagmask);
+}
+
 static __always_inline void vma_flags_set_mask(vma_flags_t *flags, vma_flags_t to_set)
 {
 	unsigned long *bitmap = flags->__vma_flags;
@@ -1031,6 +1046,12 @@ static __always_inline bool vma_test_all_mask(const struct vm_area_struct *vma,
 #define vma_test_all(vma, ...) \
 	vma_test_all_mask(vma, mk_vma_flags(__VA_ARGS__))
 
+static __always_inline bool
+vma_test_single_mask(const struct vm_area_struct *vma, vma_flags_t flagmask)
+{
+	return vma_flags_test_single_mask(&vma->flags, flagmask);
+}
+
 static __always_inline void vma_set_flags_mask(struct vm_area_struct *vma,
 		vma_flags_t flags)
 {
diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
index 0e1121e2ef23..e12ab2c80f95 100644
--- a/tools/testing/vma/vma_internal.h
+++ b/tools/testing/vma/vma_internal.h
@@ -51,6 +51,12 @@ typedef unsigned long	pgprotval_t;
 typedef struct pgprot { pgprotval_t pgprot; } pgprot_t;
 typedef __bitwise unsigned int vm_fault_t;
 
+#define VM_WARN_ON(_expr) (WARN_ON(_expr))
+#define VM_WARN_ON_ONCE(_expr) (WARN_ON_ONCE(_expr))
+#define VM_WARN_ON_VMG(_expr, _vmg) (WARN_ON(_expr))
+#define VM_BUG_ON(_expr) (BUG_ON(_expr))
+#define VM_BUG_ON_VMA(_expr, _vma) (BUG_ON(_expr))
+
 #include "include/stubs.h"
 #include "include/dup.h"
 #include "include/custom.h"
-- 
2.53.0