It's not used, we could remove it to avoid a W1 warning:
arch/x86/mm/tlb.c:318:6: warning: variable ‘cpu’ set but not used
[-Wunused-but-set-variable]

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com> 
Cc: Andy Lutomirski <luto@kernel.org> 
Cc: x86@kernel.org 
Cc: "H. Peter Anvin" <hpa@zytor.com> 
Cc: linux-kernel@vger.kernel.org 
---
 arch/x86/mm/tlb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 88e9ad5142e4..be2e9080ca79 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -315,7 +315,7 @@ void leave_mm(int cpu)
 
 int enable_l1d_flush_for_task(struct task_struct *tsk)
 {
-	int cpu, ret = 0, i;
+	int ret = 0, i;
 
 	/*
 	 * Do not enable L1D_FLUSH_OUT if
@@ -328,7 +328,7 @@ int enable_l1d_flush_for_task(struct task_struct *tsk)
 			!static_cpu_has(X86_FEATURE_FLUSH_L1D))
 		return -EINVAL;
 
-	cpu = get_cpu();
+	get_cpu();
 
 	for_each_cpu(i, &tsk->cpus_mask) {
 		if (cpu_data(i).smt_active == true) {
-- 
1.8.3.1