mm: create the new vm_fault_t type

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.

[jrdr.linux@gmail.com: fix warnings]
  Link: http://lkml.kernel.org/r/20190109183742.GA24326@jordon-HP-15-Notebook-PC
Link: http://lkml.kernel.org/r/20190108183041.GA12137@jordon-HP-15-Notebook-PC
Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 72 insertions, 1 deletions

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index ab9b48420200..86e7a7a46353 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;
@@ -621,6 +620,78 @@ 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]". */