The barrier_nospec() in 34-bit __get_user() is slow.  Instead use
pointer masking to force the user pointer to all 1's if the access_ok()
mispredicted true for an invalid address.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/x86/lib/getuser.S | 18 ------------------
 1 file changed, 18 deletions(-)

diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index 5bce27670baa..7da4fc75eba9 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -35,8 +35,6 @@
 #include <asm/asm.h>
 #include <asm/smap.h>
 
-#define ASM_BARRIER_NOSPEC ALTERNATIVE "", "lfence", X86_FEATURE_LFENCE_RDTSC
-
 .macro mask_user_address size:req
 .if IS_ENABLED(CONFIG_X86_64)
 	movq $0x0123456789abcdef,%rdx
@@ -107,11 +105,7 @@ EXPORT_SYMBOL(__get_user_8)
 
 /* .. and the same for __get_user, just without the range checks */
 SYM_FUNC_START(__get_user_nocheck_1)
-#ifdef CONFIG_X86_64
 	mask_user_address size=1
-#else
-	ASM_BARRIER_NOSPEC
-#endif
 	ASM_STAC
 	UACCESS movzbl (%_ASM_AX),%edx
 	xor %eax,%eax
@@ -121,11 +115,7 @@ SYM_FUNC_END(__get_user_nocheck_1)
 EXPORT_SYMBOL(__get_user_nocheck_1)
 
 SYM_FUNC_START(__get_user_nocheck_2)
-#ifdef CONFIG_X86_64
 	mask_user_address size=2
-#else
-	ASM_BARRIER_NOSPEC
-#endif
 	ASM_STAC
 	UACCESS movzwl (%_ASM_AX),%edx
 	xor %eax,%eax
@@ -135,11 +125,7 @@ SYM_FUNC_END(__get_user_nocheck_2)
 EXPORT_SYMBOL(__get_user_nocheck_2)
 
 SYM_FUNC_START(__get_user_nocheck_4)
-#ifdef CONFIG_X86_64
 	mask_user_address size=4
-#else
-	ASM_BARRIER_NOSPEC
-#endif
 	ASM_STAC
 	UACCESS movl (%_ASM_AX),%edx
 	xor %eax,%eax
@@ -149,11 +135,7 @@ SYM_FUNC_END(__get_user_nocheck_4)
 EXPORT_SYMBOL(__get_user_nocheck_4)
 
 SYM_FUNC_START(__get_user_nocheck_8)
-#ifdef CONFIG_X86_64
 	mask_user_address size=8
-#else
-	ASM_BARRIER_NOSPEC
-#endif
 	ASM_STAC
 #ifdef CONFIG_X86_64
 	UACCESS movq (%_ASM_AX),%rdx
-- 
2.47.0