Revert "x86/copy_mc: Introduce copy_mc_enhanced_fast_string()"

This reverts commit 4f28b1f which is
commit 5da8e4a upstream.

We had a mistake when merging a later patch in this series due to some
file movements, so revert this change for now, as we will add it back in
a later commit.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/lib/copy_mc.c

@@ -45,20 +45,16 @@ void enable_copy_mc_fragile(void)
 #define copy_mc_fragile_enabled (0)
 #endif
 
-unsigned long copy_mc_enhanced_fast_string(void *dst, const void *src, unsigned len);
-
 /**
  * copy_mc_to_kernel - memory copy that handles source exceptions
  *
  * @dst:	destination address
  * @src:	source address
  * @len:	number of bytes to copy
  *
- * Call into the 'fragile' version on systems that benefit from avoiding
- * corner case poison consumption scenarios, For example, accessing
- * poison across 2 cachelines with a single instruction. Almost all
- * other uses case can use copy_mc_enhanced_fast_string() for a fast
- * recoverable copy, or fallback to plain memcpy.
+ * Call into the 'fragile' version on systems that have trouble
+ * actually do machine check recovery. Everyone else can just
+ * use memcpy().
  *
  * Return 0 for success, or number of bytes not copied if there was an
  * exception.
@@ -67,8 +63,6 @@ unsigned long __must_check copy_mc_to_kernel(void *dst, const void *src, unsigne
 {
 	if (copy_mc_fragile_enabled)
 		return copy_mc_fragile(dst, src, len);
-	if (static_cpu_has(X86_FEATURE_ERMS))
-		return copy_mc_enhanced_fast_string(dst, src, len);
 	memcpy(dst, src, len);
 	return 0;
 }
@@ -78,19 +72,11 @@ unsigned long __must_check copy_mc_to_user(void *dst, const void *src, unsigned
 {
 	unsigned long ret;
 
-	if (copy_mc_fragile_enabled) {
-		__uaccess_begin();
-		ret = copy_mc_fragile(dst, src, len);
-		__uaccess_end();
-		return ret;
-	}
-
-	if (static_cpu_has(X86_FEATURE_ERMS)) {
-		__uaccess_begin();
-		ret = copy_mc_enhanced_fast_string(dst, src, len);
-		__uaccess_end();
-		return ret;
-	}
+	if (!copy_mc_fragile_enabled)
+		return copy_user_generic(dst, src, len);
 
-	return copy_user_generic(dst, src, len);
+	__uaccess_begin();
+	ret = copy_mc_fragile(dst, src, len);
+	__uaccess_end();
+	return ret;
 }

arch/x86/lib/copy_mc_64.S

@@ -124,40 +124,4 @@ EXPORT_SYMBOL_GPL(copy_mc_fragile)
 	_ASM_EXTABLE(.L_write_words, .E_write_words)
 	_ASM_EXTABLE(.L_write_trailing_bytes, .E_trailing_bytes)
 #endif /* CONFIG_X86_MCE */
-
-/*
- * copy_mc_enhanced_fast_string - memory copy with exception handling
- *
- * Fast string copy + fault / exception handling. If the CPU does
- * support machine check exception recovery, but does not support
- * recovering from fast-string exceptions then this CPU needs to be
- * added to the copy_mc_fragile_key set of quirks. Otherwise, absent any
- * machine check recovery support this version should be no slower than
- * standard memcpy.
- */
-SYM_FUNC_START(copy_mc_enhanced_fast_string)
-	movq %rdi, %rax
-	movq %rdx, %rcx
-.L_copy:
-	rep movsb
-	/* Copy successful. Return zero */
-	xorl %eax, %eax
-	ret
-SYM_FUNC_END(copy_mc_enhanced_fast_string)
-
-	.section .fixup, "ax"
-.E_copy:
-	/*
-	 * On fault %rcx is updated such that the copy instruction could
-	 * optionally be restarted at the fault position, i.e. it
-	 * contains 'bytes remaining'. A non-zero return indicates error
-	 * to copy_mc_generic() users, or indicate short transfers to
-	 * user-copy routines.
-	 */
-	movq %rcx, %rax
-	ret
-
-	.previous
-
-	_ASM_EXTABLE_FAULT(.L_copy, .E_copy)
 #endif /* !CONFIG_UML */

tools/objtool/check.c

@@ -550,7 +550,6 @@ static const char *uaccess_safe_builtin[] = {
 	"csum_partial_copy_generic",
 	"copy_mc_fragile",
 	"copy_mc_fragile_handle_tail",
-	"copy_mc_enhanced_fast_string",
 	"ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 	NULL
 };