amd64: get rid of zeroing

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/x86/include/asm/uaccess.h

@@ -379,6 +379,18 @@ do {									\
 		     : "=r" (err), ltype(x)				\
 		     : "m" (__m(addr)), "i" (errret), "0" (err))
 
+#define __get_user_asm_nozero(x, addr, err, itype, rtype, ltype, errret)	\
+	asm volatile("\n"						\
+		     "1:	mov"itype" %2,%"rtype"1\n"		\
+		     "2:\n"						\
+		     ".section .fixup,\"ax\"\n"				\
+		     "3:	mov %3,%0\n"				\
+		     "	jmp 2b\n"					\
+		     ".previous\n"					\
+		     _ASM_EXTABLE(1b, 3b)				\
+		     : "=r" (err), ltype(x)				\
+		     : "m" (__m(addr)), "i" (errret), "0" (err))
+
 /*
  * This doesn't do __uaccess_begin/end - the exception handling
  * around it must do that.

arch/x86/include/asm/uaccess_64.h

@@ -59,44 +59,44 @@ int __copy_from_user_nocheck(void *dst, const void __user *src, unsigned size)
 	switch (size) {
 	case 1:
 		__uaccess_begin();
-		__get_user_asm(*(u8 *)dst, (u8 __user *)src,
+		__get_user_asm_nozero(*(u8 *)dst, (u8 __user *)src,
 			      ret, "b", "b", "=q", 1);
 		__uaccess_end();
 		return ret;
 	case 2:
 		__uaccess_begin();
-		__get_user_asm(*(u16 *)dst, (u16 __user *)src,
+		__get_user_asm_nozero(*(u16 *)dst, (u16 __user *)src,
 			      ret, "w", "w", "=r", 2);
 		__uaccess_end();
 		return ret;
 	case 4:
 		__uaccess_begin();
-		__get_user_asm(*(u32 *)dst, (u32 __user *)src,
+		__get_user_asm_nozero(*(u32 *)dst, (u32 __user *)src,
 			      ret, "l", "k", "=r", 4);
 		__uaccess_end();
 		return ret;
 	case 8:
 		__uaccess_begin();
-		__get_user_asm(*(u64 *)dst, (u64 __user *)src,
+		__get_user_asm_nozero(*(u64 *)dst, (u64 __user *)src,
 			      ret, "q", "", "=r", 8);
 		__uaccess_end();
 		return ret;
 	case 10:
 		__uaccess_begin();
-		__get_user_asm(*(u64 *)dst, (u64 __user *)src,
+		__get_user_asm_nozero(*(u64 *)dst, (u64 __user *)src,
 			       ret, "q", "", "=r", 10);
 		if (likely(!ret))
-			__get_user_asm(*(u16 *)(8 + (char *)dst),
+			__get_user_asm_nozero(*(u16 *)(8 + (char *)dst),
 				       (u16 __user *)(8 + (char __user *)src),
 				       ret, "w", "w", "=r", 2);
 		__uaccess_end();
 		return ret;
 	case 16:
 		__uaccess_begin();
-		__get_user_asm(*(u64 *)dst, (u64 __user *)src,
+		__get_user_asm_nozero(*(u64 *)dst, (u64 __user *)src,
 			       ret, "q", "", "=r", 16);
 		if (likely(!ret))
-			__get_user_asm(*(u64 *)(8 + (char *)dst),
+			__get_user_asm_nozero(*(u64 *)(8 + (char *)dst),
 				       (u64 __user *)(8 + (char __user *)src),
 				       ret, "q", "", "=r", 8);
 		__uaccess_end();

arch/x86/lib/usercopy.c

@@ -76,10 +76,11 @@ EXPORT_SYMBOL(_copy_to_user);
  */
 unsigned long _copy_from_user(void *to, const void __user *from, unsigned n)
 {
+	unsigned long res = n;
 	if (access_ok(VERIFY_READ, from, n))
-		n = __copy_from_user(to, from, n);
-	else
-		memset(to, 0, n);
-	return n;
+		res = __copy_from_user_inatomic(to, from, n);
+	if (unlikely(res))
+		memset(to + n - res, 0, res);
+	return res;
 }
 EXPORT_SYMBOL(_copy_from_user);

arch/x86/lib/usercopy_64.c

@@ -80,9 +80,5 @@ copy_user_handle_tail(char *to, char *from, unsigned len)
 			break;
 	}
 	clac();
-
-	/* If the destination is a kernel buffer, we always clear the end */
-	if (!__addr_ok(to))
-		memset(to, 0, len);
 	return len;
 }