1 files changed, 33 insertions, 0 deletions

diff --git a/arch/x86/include/asm/word-at-a-time.h b/arch/x86/include/asm/word-at-a-time.h
index 6fe6767b7124..e58f03b206c3 100644
--- a/arch/x86/include/asm/word-at-a-time.h
+++ b/arch/x86/include/asm/word-at-a-time.h
@@ -43,4 +43,37 @@ static inline unsigned long has_zero(unsigned long a)
         return ((a - REPEAT_BYTE(0x01)) & ~a) & REPEAT_BYTE(0x80);
 }
 
+/*
+ * Load an unaligned word from kernel space.
+ *
+ * In the (very unlikely) case of the word being a page-crosser
+ * and the next page not being mapped, take the exception and
+ * return zeroes in the non-existing part.
+ */
+static inline unsigned long load_unaligned_zeropad(const void *addr)
+{
+        unsigned long ret, dummy;
+
+        asm(
+                "1:\tmov %2,%0\n"
+                "2:\n"
+                ".section .fixup,\"ax\"\n"
+                "3:\t"
+                "lea %2,%1\n\t"
+                "and %3,%1\n\t"
+                "mov (%1),%0\n\t"
+                "leal %2,%%ecx\n\t"
+                "andl %4,%%ecx\n\t"
+                "shll $3,%%ecx\n\t"
+                "shr %%cl,%0\n\t"
+                "jmp 2b\n"
+                ".previous\n"
+                _ASM_EXTABLE(1b, 3b)
+                :"=&r" (ret),"=&c" (dummy)
+                :"m" (*(unsigned long *)addr),
+                 "i" (-sizeof(unsigned long)),
+                 "i" (sizeof(unsigned long)-1));
+        return ret;
+}
+
 #endif /* _ASM_WORD_AT_A_TIME_H */