[PATCH] Make copy_from_user_inatomic NOT zero the tail on i386

As described in a previous patch and documented in mm/filemap.h,
copy_from_user_inatomic* shouldn't zero out the tail of the buffer after an
incomplete copy.

This patch implements that change for i386.

For the _nocache version, a new __copy_user_intel_nocache is defined similar
to copy_user_zeroio_intel_nocache, and this is ultimately used for the copy.

For the regular version, __copy_from_user_ll_nozero is defined which uses
__copy_user and __copy_user_intel - the later needs casts to reposition the
__user annotations.

If copy_from_user_atomic is given a constant length of 1, 2, or 4, then we do
still zero the destintion on failure. This didn't seem worth the effort of
fixing as the places where it is used really don't care.

Signed-off-by: Neil Brown <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: William Lee Irwin III <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/i386/lib/usercopy.c

···
 	return size;
 }
 
+static unsigned long __copy_user_intel_nocache(void *to,
+				const void __user *from, unsigned long size)
+{
+        int d0, d1;
+
+	__asm__ __volatile__(
+	       "        .align 2,0x90\n"
+	       "0:      movl 32(%4), %%eax\n"
+	       "        cmpl $67, %0\n"
+	       "        jbe 2f\n"
+	       "1:      movl 64(%4), %%eax\n"
+	       "        .align 2,0x90\n"
+	       "2:      movl 0(%4), %%eax\n"
+	       "21:     movl 4(%4), %%edx\n"
+	       "        movnti %%eax, 0(%3)\n"
+	       "        movnti %%edx, 4(%3)\n"
+	       "3:      movl 8(%4), %%eax\n"
+	       "31:     movl 12(%4),%%edx\n"
+	       "        movnti %%eax, 8(%3)\n"
+	       "        movnti %%edx, 12(%3)\n"
+	       "4:      movl 16(%4), %%eax\n"
+	       "41:     movl 20(%4), %%edx\n"
+	       "        movnti %%eax, 16(%3)\n"
+	       "        movnti %%edx, 20(%3)\n"
+	       "10:     movl 24(%4), %%eax\n"
+	       "51:     movl 28(%4), %%edx\n"
+	       "        movnti %%eax, 24(%3)\n"
+	       "        movnti %%edx, 28(%3)\n"
+	       "11:     movl 32(%4), %%eax\n"
+	       "61:     movl 36(%4), %%edx\n"
+	       "        movnti %%eax, 32(%3)\n"
+	       "        movnti %%edx, 36(%3)\n"
+	       "12:     movl 40(%4), %%eax\n"
+	       "71:     movl 44(%4), %%edx\n"
+	       "        movnti %%eax, 40(%3)\n"
+	       "        movnti %%edx, 44(%3)\n"
+	       "13:     movl 48(%4), %%eax\n"
+	       "81:     movl 52(%4), %%edx\n"
+	       "        movnti %%eax, 48(%3)\n"
+	       "        movnti %%edx, 52(%3)\n"
+	       "14:     movl 56(%4), %%eax\n"
+	       "91:     movl 60(%4), %%edx\n"
+	       "        movnti %%eax, 56(%3)\n"
+	       "        movnti %%edx, 60(%3)\n"
+	       "        addl $-64, %0\n"
+	       "        addl $64, %4\n"
+	       "        addl $64, %3\n"
+	       "        cmpl $63, %0\n"
+	       "        ja  0b\n"
+	       "        sfence \n"
+	       "5:      movl  %0, %%eax\n"
+	       "        shrl  $2, %0\n"
+	       "        andl $3, %%eax\n"
+	       "        cld\n"
+	       "6:      rep; movsl\n"
+	       "        movl %%eax,%0\n"
+	       "7:      rep; movsb\n"
+	       "8:\n"
+	       ".section .fixup,\"ax\"\n"
+	       "9:      lea 0(%%eax,%0,4),%0\n"
+	       "16:     jmp 8b\n"
+	       ".previous\n"
+	       ".section __ex_table,\"a\"\n"
+	       "	.align 4\n"
+	       "	.long 0b,16b\n"
+	       "	.long 1b,16b\n"
+	       "	.long 2b,16b\n"
+	       "	.long 21b,16b\n"
+	       "	.long 3b,16b\n"
+	       "	.long 31b,16b\n"
+	       "	.long 4b,16b\n"
+	       "	.long 41b,16b\n"
+	       "	.long 10b,16b\n"
+	       "	.long 51b,16b\n"
+	       "	.long 11b,16b\n"
+	       "	.long 61b,16b\n"
+	       "	.long 12b,16b\n"
+	       "	.long 71b,16b\n"
+	       "	.long 13b,16b\n"
+	       "	.long 81b,16b\n"
+	       "	.long 14b,16b\n"
+	       "	.long 91b,16b\n"
+	       "	.long 6b,9b\n"
+	       "        .long 7b,16b\n"
+	       ".previous"
+	       : "=&c"(size), "=&D" (d0), "=&S" (d1)
+	       :  "1"(to), "2"(from), "0"(size)
+	       : "eax", "edx", "memory");
+	return size;
+}
+
 #else
 
 /*
···
 }
 EXPORT_SYMBOL(__copy_from_user_ll);
 
+unsigned long __copy_from_user_ll_nozero(void *to, const void __user *from,
+					 unsigned long n)
+{
+	BUG_ON((long)n < 0);
+	if (movsl_is_ok(to, from, n))
+		__copy_user(to, from, n);
+	else
+		n = __copy_user_intel((void __user *)to,
+				      (const void *)from, n);
+	return n;
+}
+EXPORT_SYMBOL(__copy_from_user_ll_nozero);
+
 unsigned long __copy_from_user_ll_nocache(void *to, const void __user *from,
 					unsigned long n)
 {
···
 		__copy_user_zeroing(to, from, n);
 #else
         __copy_user_zeroing(to, from, n);
+#endif
+	return n;
+}
+
+unsigned long __copy_from_user_ll_nocache_nozero(void *to, const void __user *from,
+					unsigned long n)
+{
+	BUG_ON((long)n < 0);
+#ifdef CONFIG_X86_INTEL_USERCOPY
+	if ( n > 64 && cpu_has_xmm2)
+                n = __copy_user_intel_nocache(to, from, n);
+	else
+		__copy_user(to, from, n);
+#else
+        __copy_user(to, from, n);
 #endif
 	return n;
 }

include/asm-i386/uaccess.h

···
 				const void *from, unsigned long n);
 unsigned long __must_check __copy_from_user_ll(void *to,
 				const void __user *from, unsigned long n);
+unsigned long __must_check __copy_from_user_ll_nozero(void *to,
+				const void __user *from, unsigned long n);
 unsigned long __must_check __copy_from_user_ll_nocache(void *to,
+				const void __user *from, unsigned long n);
+unsigned long __must_check __copy_from_user_ll_nocache_nozero(void *to,
 				const void __user *from, unsigned long n);
 
 /*
···
  * atomic context and will fail rather than sleep.  In this case the
  * uncopied bytes will *NOT* be padded with zeros.  See fs/filemap.h
  * for explanation of why this is needed.
- * FIXME this isn't implimented yet EMXIF
  */
 static __always_inline unsigned long
 __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
 {
+	/* Avoid zeroing the tail if the copy fails..
+	 * If 'n' is constant and 1, 2, or 4, we do still zero on a failure,
+	 * but as the zeroing behaviour is only significant when n is not
+	 * constant, that shouldn't be a problem.
+	 */
+	if (__builtin_constant_p(n)) {
+		unsigned long ret;
+
+		switch (n) {
+		case 1:
+			__get_user_size(*(u8 *)to, from, 1, ret, 1);
+			return ret;
+		case 2:
+			__get_user_size(*(u16 *)to, from, 2, ret, 2);
+			return ret;
+		case 4:
+			__get_user_size(*(u32 *)to, from, 4, ret, 4);
+			return ret;
+		}
+	}
+	return __copy_from_user_ll_nozero(to, from, n);
+}
+static __always_inline unsigned long
+__copy_from_user(void *to, const void __user *from, unsigned long n)
+{
+	might_sleep();
 	if (__builtin_constant_p(n)) {
 		unsigned long ret;
 
···
 
 #define ARCH_HAS_NOCACHE_UACCESS
 
-static __always_inline unsigned long __copy_from_user_inatomic_nocache(void *to,
+static __always_inline unsigned long __copy_from_user_nocache(void *to,
 				const void __user *from, unsigned long n)
 {
+	might_sleep();
 	if (__builtin_constant_p(n)) {
 		unsigned long ret;
 
···
 }
 
 static __always_inline unsigned long
-__copy_from_user(void *to, const void __user *from, unsigned long n)
+__copy_from_user_inatomic_nocache(void *to, const void __user *from, unsigned long n)
 {
-       might_sleep();
-       return __copy_from_user_inatomic(to, from, n);
-}
-
-static __always_inline unsigned long
-__copy_from_user_nocache(void *to, const void __user *from, unsigned long n)
-{
-       might_sleep();
-       return __copy_from_user_inatomic_nocache(to, from, n);
+       return __copy_from_user_ll_nocache_nozero(to, from, n);
 }
 
 unsigned long __must_check copy_to_user(void __user *to,