linux-kernel - [PATCH -next for tip:x86/pti] x86/tlb: drop unneeded local vars in enable_l1d_flush_for

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Message-Id: <20200928124457.27289-1-lukas.bulwahn@gmail.com>
Date:   Mon, 28 Sep 2020 14:44:57 +0200
From:   Lukas Bulwahn <lukas.bulwahn@...il.com>
To:     Balbir Singh <sblbir@...zon.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        kernel-janitors@...r.kernel.org, linux-safety@...ts.elisa.tech,
        Lukas Bulwahn <lukas.bulwahn@...il.com>
Subject: [PATCH -next for tip:x86/pti] x86/tlb: drop unneeded local vars in enable_l1d_flush_for_task()

Commit b6724f118d44 ("prctl: Hook L1D flushing in via prctl") checks the
validity for enable_l1d_flush_for_task() and introduces some superfluous
local variables for that implementation.

make clang-analyzer on x86_64 tinyconfig caught my attention with:

  arch/x86/mm/tlb.c:332:2: warning: Value stored to 'cpu' is never read \
  [clang-analyzer-deadcode.DeadStores]

Compilers will detect these superfluous local variables and assignment and
optimize this anyway. So, the resulting binary is identical before and
after this change.

Simplify the code and remove superfluous local variables to make
clang-analyzer happy.

No functional change. No change in binary with supported compilers.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@...il.com>
---
applies cleanly on next-20200925

Balbir, please review and ack.
Thomas, please pick this minor non-urgent clean-up patch into the x86/pti
branch of tip as follow-up to: 
https://lore.kernel.org/lkml/160026187842.15536.285514864386042510.tip-bot2@tip-bot2/

I quickly confirmed that the binary did not change with this change to the
source code; The hash of tlb.o remained the same before and after the change.

So, in my setup:
md5sum tlb.o
7c7e096bab0fd87bd2c8437d8c7dc3fa  tlb.o

linux-safety, please verify and validate this change.

 arch/x86/mm/tlb.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 6b0f4c88b07c..90515c04d90a 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -316,7 +316,7 @@ EXPORT_SYMBOL_GPL(leave_mm);
 
 int enable_l1d_flush_for_task(struct task_struct *tsk)
 {
-	int cpu, ret = 0, i;
+	int i;
 
 	/*
 	 * Do not enable L1D_FLUSH_OUT if
@@ -329,7 +329,7 @@ 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) {
@@ -340,7 +340,7 @@ int enable_l1d_flush_for_task(struct task_struct *tsk)
 
 	set_ti_thread_flag(&tsk->thread_info, TIF_SPEC_L1D_FLUSH);
 	put_cpu();
-	return ret;
+	return 0;
 }
 
 int disable_l1d_flush_for_task(struct task_struct *tsk)
-- 
2.17.1