3 files changed, 80 insertions, 33 deletions

diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 01932af64193..ea3a28e7b613 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -61,8 +61,9 @@ ifeq ($(CONFIG_X86_32),y)
         lib-y += strstr_32.o
         lib-y += string_32.o
         lib-y += memmove_32.o
+        lib-y += cmpxchg8b_emu.o
 ifneq ($(CONFIG_X86_CMPXCHG64),y)
-        lib-y += cmpxchg8b_emu.o atomic64_386_32.o
+        lib-y += atomic64_386_32.o
 endif
 else
         obj-y += iomap_copy_64.o
diff --git a/arch/x86/lib/cmpxchg16b_emu.S b/arch/x86/lib/cmpxchg16b_emu.S
index 33c70c0160ea..6962df315793 100644
--- a/arch/x86/lib/cmpxchg16b_emu.S
+++ b/arch/x86/lib/cmpxchg16b_emu.S
@@ -1,47 +1,54 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 #include <linux/linkage.h>
 #include <asm/percpu.h>
+#include <asm/processor-flags.h>
 
 .text
 
 /*
+ * Emulate 'cmpxchg16b %gs:(%rsi)'
+ *
  * Inputs:
  * %rsi : memory location to compare
  * %rax : low 64 bits of old value
  * %rdx : high 64 bits of old value
  * %rbx : low 64 bits of new value
  * %rcx : high 64 bits of new value
- * %al  : Operation successful
+ *
+ * Notably this is not LOCK prefixed and is not safe against NMIs
  */
 SYM_FUNC_START(this_cpu_cmpxchg16b_emu)
 
-#
-# Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in %al not
-# via the ZF.  Caller will access %al to get result.
-#
-# Note that this is only useful for a cpuops operation.  Meaning that we
-# do *not* have a fully atomic operation but just an operation that is
-# *atomic* on a single cpu (as provided by the this_cpu_xx class of
-# macros).
-#
 	pushfq
 	cli
 
-	cmpq PER_CPU_VAR((%rsi)), %rax
-	jne .Lnot_same
-	cmpq PER_CPU_VAR(8(%rsi)), %rdx
-	jne .Lnot_same
+	/* if (*ptr == old) */
+	cmpq	PER_CPU_VAR(0(%rsi)), %rax
+	jne	.Lnot_same
+	cmpq	PER_CPU_VAR(8(%rsi)), %rdx
+	jne	.Lnot_same
 
-	movq %rbx, PER_CPU_VAR((%rsi))
-	movq %rcx, PER_CPU_VAR(8(%rsi))
+	/* *ptr = new */
+	movq	%rbx, PER_CPU_VAR(0(%rsi))
+	movq	%rcx, PER_CPU_VAR(8(%rsi))
+
+	/* set ZF in EFLAGS to indicate success */
+	orl	$X86_EFLAGS_ZF, (%rsp)
 
 	popfq
-	mov $1, %al
 	RET
 
 .Lnot_same:
+	/* *ptr != old */
+
+	/* old = *ptr */
+	movq	PER_CPU_VAR(0(%rsi)), %rax
+	movq	PER_CPU_VAR(8(%rsi)), %rdx
+
+	/* clear ZF in EFLAGS to indicate failure */
+	andl	$(~X86_EFLAGS_ZF), (%rsp)
+
 	popfq
-	xor %al,%al
 	RET
 
 SYM_FUNC_END(this_cpu_cmpxchg16b_emu)
diff --git a/arch/x86/lib/cmpxchg8b_emu.S b/arch/x86/lib/cmpxchg8b_emu.S
index 6a912d58fecc..49805257b125 100644
--- a/arch/x86/lib/cmpxchg8b_emu.S
+++ b/arch/x86/lib/cmpxchg8b_emu.S
@@ -2,10 +2,16 @@
 
 #include <linux/linkage.h>
 #include <asm/export.h>
+#include <asm/percpu.h>
+#include <asm/processor-flags.h>
 
 .text
 
+#ifndef CONFIG_X86_CMPXCHG64
+
 /*
+ * Emulate 'cmpxchg8b (%esi)' on UP
+ *
  * Inputs:
  * %esi : memory location to compare
  * %eax : low 32 bits of old value
@@ -15,32 +21,65 @@
  */
 SYM_FUNC_START(cmpxchg8b_emu)
 
-#
-# Emulate 'cmpxchg8b (%esi)' on UP except we don't
-# set the whole ZF thing (caller will just compare
-# eax:edx with the expected value)
-#
 	pushfl
 	cli
 
-	cmpl  (%esi), %eax
-	jne .Lnot_same
-	cmpl 4(%esi), %edx
-	jne .Lhalf_same
+	cmpl	0(%esi), %eax
+	jne	.Lnot_same
+	cmpl	4(%esi), %edx
+	jne	.Lnot_same
+
+	movl	%ebx, 0(%esi)
+	movl	%ecx, 4(%esi)
 
-	movl %ebx,  (%esi)
-	movl %ecx, 4(%esi)
+	orl	$X86_EFLAGS_ZF, (%esp)
 
 	popfl
 	RET
 
 .Lnot_same:
-	movl  (%esi), %eax
-.Lhalf_same:
-	movl 4(%esi), %edx
+	movl	0(%esi), %eax
+	movl	4(%esi), %edx
+
+	andl	$(~X86_EFLAGS_ZF), (%esp)
 
 	popfl
 	RET
 
 SYM_FUNC_END(cmpxchg8b_emu)
 EXPORT_SYMBOL(cmpxchg8b_emu)
+
+#endif
+
+#ifndef CONFIG_UML
+
+SYM_FUNC_START(this_cpu_cmpxchg8b_emu)
+
+	pushfl
+	cli
+
+	cmpl	PER_CPU_VAR(0(%esi)), %eax
+	jne	.Lnot_same2
+	cmpl	PER_CPU_VAR(4(%esi)), %edx
+	jne	.Lnot_same2
+
+	movl	%ebx, PER_CPU_VAR(0(%esi))
+	movl	%ecx, PER_CPU_VAR(4(%esi))
+
+	orl	$X86_EFLAGS_ZF, (%esp)
+
+	popfl
+	RET
+
+.Lnot_same2:
+	movl	PER_CPU_VAR(0(%esi)), %eax
+	movl	PER_CPU_VAR(4(%esi)), %edx
+
+	andl	$(~X86_EFLAGS_ZF), (%esp)
+
+	popfl
+	RET
+
+SYM_FUNC_END(this_cpu_cmpxchg8b_emu)
+
+#endif