[PATCH v3] mm: Create the new vm_fault_t type

[Souptick Joarder <jrdr.linux@gmail.com>]

Page fault handlers are supposed to return VM_FAULT codes,
but some drivers/file systems mistakenly return error
numbers. Now that all drivers/file systems have been converted
to use the vm_fault_t return type, change the type definition
to no longer be compatible with 'int'. By making it an unsigned
int, the function prototype becomes incompatible with a function
which returns int. Sparse will detect any attempts to return a
value which is not a VM_FAULT code.

VM_FAULT_SET_HINDEX and VM_FAULT_GET_HINDEX values are changed
to avoid conflict with other VM_FAULT codes.

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
---
v2: Updated the change log and corrected the document part.
    name added to the enum that kernel-doc able to parse it.

v3: Corrected the documentation.

 include/linux/mm.h       | 46 ------------------------------
 include/linux/mm_types.h | 73 +++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 72 insertions(+), 47 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index fcf9cc9..511a3ce 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1267,52 +1267,6 @@ static inline void clear_page_pfmemalloc(struct page *page)
 }
 
 /*
- * Different kinds of faults, as returned by handle_mm_fault().
- * Used to decide whether a process gets delivered SIGBUS or
- * just gets major/minor fault counters bumped up.
- */
-
-#define VM_FAULT_OOM	0x0001
-#define VM_FAULT_SIGBUS	0x0002
-#define VM_FAULT_MAJOR	0x0004
-#define VM_FAULT_WRITE	0x0008	/* Special case for get_user_pages */
-#define VM_FAULT_HWPOISON 0x0010	/* Hit poisoned small page */
-#define VM_FAULT_HWPOISON_LARGE 0x0020  /* Hit poisoned large page. Index encoded in upper bits */
-#define VM_FAULT_SIGSEGV 0x0040
-
-#define VM_FAULT_NOPAGE	0x0100	/* ->fault installed the pte, not return page */
-#define VM_FAULT_LOCKED	0x0200	/* ->fault locked the returned page */
-#define VM_FAULT_RETRY	0x0400	/* ->fault blocked, must retry */
-#define VM_FAULT_FALLBACK 0x0800	/* huge page fault failed, fall back to small */
-#define VM_FAULT_DONE_COW   0x1000	/* ->fault has fully handled COW */
-#define VM_FAULT_NEEDDSYNC  0x2000	/* ->fault did not modify page tables
-					 * and needs fsync() to complete (for
-					 * synchronous page faults in DAX) */
-
-#define VM_FAULT_ERROR	(VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | \
-			 VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE | \
-			 VM_FAULT_FALLBACK)
-
-#define VM_FAULT_RESULT_TRACE \
-	{ VM_FAULT_OOM,			"OOM" }, \
-	{ VM_FAULT_SIGBUS,		"SIGBUS" }, \
-	{ VM_FAULT_MAJOR,		"MAJOR" }, \
-	{ VM_FAULT_WRITE,		"WRITE" }, \
-	{ VM_FAULT_HWPOISON,		"HWPOISON" }, \
-	{ VM_FAULT_HWPOISON_LARGE,	"HWPOISON_LARGE" }, \
-	{ VM_FAULT_SIGSEGV,		"SIGSEGV" }, \
-	{ VM_FAULT_NOPAGE,		"NOPAGE" }, \
-	{ VM_FAULT_LOCKED,		"LOCKED" }, \
-	{ VM_FAULT_RETRY,		"RETRY" }, \
-	{ VM_FAULT_FALLBACK,		"FALLBACK" }, \
-	{ VM_FAULT_DONE_COW,		"DONE_COW" }, \
-	{ VM_FAULT_NEEDDSYNC,		"NEEDDSYNC" }
-
-/* Encode hstate index for a hwpoisoned large page */
-#define VM_FAULT_SET_HINDEX(x) ((x) << 12)
-#define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
-
-/*
  * Can be called by the pagefault handler when it gets a VM_FAULT_OOM.
  */
 extern void pagefault_out_of_memory(void);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5ed8f62..cb25016 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -22,7 +22,6 @@
 #endif
 #define AT_VECTOR_SIZE (2*(AT_VECTOR_SIZE_ARCH + AT_VECTOR_SIZE_BASE + 1))
 
-typedef int vm_fault_t;
 
 struct address_space;
 struct mem_cgroup;
@@ -609,6 +608,78 @@ static inline bool mm_tlb_flush_nested(struct mm_struct *mm)
 
 struct vm_fault;
 
+/**
+ * typedef vm_fault_t - Return type for page fault handlers.
+ *
+ * Page fault handlers return a bitmask of %VM_FAULT values.
+ */
+typedef __bitwise unsigned int vm_fault_t;
+
+/**
+ * enum vm_fault_reason - Page fault handlers return a bitmask of
+ * these values to tell the core VM what happened when handling the
+ * fault. Used to decide whether a process gets delivered SIGBUS or
+ * just gets major/minor fault counters bumped up.
+ *
+ * @VM_FAULT_OOM:		Out Of Memory
+ * @VM_FAULT_SIGBUS:		Bad access
+ * @VM_FAULT_MAJOR:		Page read from storage
+ * @VM_FAULT_WRITE:		Special case for get_user_pages
+ * @VM_FAULT_HWPOISON:		Hit poisoned small page
+ * @VM_FAULT_HWPOISON_LARGE:	Hit poisoned large page. Index encoded
+ *				in upper bits
+ * @VM_FAULT_SIGSEGV:		segmentation fault
+ * @VM_FAULT_NOPAGE:		->fault installed the pte, not return page
+ * @VM_FAULT_LOCKED:		->fault locked the returned page
+ * @VM_FAULT_RETRY:		->fault blocked, must retry
+ * @VM_FAULT_FALLBACK:		huge page fault failed, fall back to small
+ * @VM_FAULT_DONE_COW:		->fault has fully handled COW
+ * @VM_FAULT_NEEDDSYNC:		->fault did not modify page tables and needs
+ *				fsync() to complete (for synchronous page faults
+ *				in DAX)
+ * @VM_FAULT_HINDEX_MASK:	mask HINDEX value
+ *
+ */
+enum vm_fault_reason {
+	VM_FAULT_OOM            = (__force vm_fault_t)0x000001,
+	VM_FAULT_SIGBUS         = (__force vm_fault_t)0x000002,
+	VM_FAULT_MAJOR          = (__force vm_fault_t)0x000004,
+	VM_FAULT_WRITE          = (__force vm_fault_t)0x000008,
+	VM_FAULT_HWPOISON       = (__force vm_fault_t)0x000010,
+	VM_FAULT_HWPOISON_LARGE = (__force vm_fault_t)0x000020,
+	VM_FAULT_SIGSEGV        = (__force vm_fault_t)0x000040,
+	VM_FAULT_NOPAGE         = (__force vm_fault_t)0x000100,
+	VM_FAULT_LOCKED         = (__force vm_fault_t)0x000200,
+	VM_FAULT_RETRY          = (__force vm_fault_t)0x000400,
+	VM_FAULT_FALLBACK       = (__force vm_fault_t)0x000800,
+	VM_FAULT_DONE_COW       = (__force vm_fault_t)0x001000,
+	VM_FAULT_NEEDDSYNC      = (__force vm_fault_t)0x002000,
+	VM_FAULT_HINDEX_MASK    = (__force vm_fault_t)0x0f0000,
+};
+
+/* Encode hstate index for a hwpoisoned large page */
+#define VM_FAULT_SET_HINDEX(x) ((__force vm_fault_t)((x) << 16))
+#define VM_FAULT_GET_HINDEX(x) (((x) >> 16) & 0xf)
+
+#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS |	\
+			VM_FAULT_SIGSEGV | VM_FAULT_HWPOISON |	\
+			VM_FAULT_HWPOISON_LARGE | VM_FAULT_FALLBACK)
+
+#define VM_FAULT_RESULT_TRACE \
+	{ VM_FAULT_OOM,                 "OOM" },	\
+	{ VM_FAULT_SIGBUS,              "SIGBUS" },	\
+	{ VM_FAULT_MAJOR,               "MAJOR" },	\
+	{ VM_FAULT_WRITE,               "WRITE" },	\
+	{ VM_FAULT_HWPOISON,            "HWPOISON" },	\
+	{ VM_FAULT_HWPOISON_LARGE,      "HWPOISON_LARGE" },	\
+	{ VM_FAULT_SIGSEGV,             "SIGSEGV" },	\
+	{ VM_FAULT_NOPAGE,              "NOPAGE" },	\
+	{ VM_FAULT_LOCKED,              "LOCKED" },	\
+	{ VM_FAULT_RETRY,               "RETRY" },	\
+	{ VM_FAULT_FALLBACK,            "FALLBACK" },	\
+	{ VM_FAULT_DONE_COW,            "DONE_COW" },	\
+	{ VM_FAULT_NEEDDSYNC,           "NEEDDSYNC" }
+
 struct vm_special_mapping {
 	const char *name;	/* The name, e.g. "[vdso]". */
 
-- 
1.9.1