linux-kernel - [tip:x86/pti] x86/cpu/AMD: Use LFENCE_RDTSC instead of MFENCE

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Date:   Sat, 6 Jan 2018 13:06:00 -0800
From:   tip-bot for Tom Lendacky <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, tim.c.chen@...ux.intel.com, peterz@...radead.org,
        dave.hansen@...el.com, torvalds@...ux-foundation.org, bp@...en8.de,
        dwmw@...zon.co.uk, tglx@...utronix.de, mingo@...nel.org,
        pjt@...gle.com, thomas.lendacky@....com,
        gregkh@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: [tip:x86/pti] x86/cpu/AMD: Use LFENCE_RDTSC instead of MFENCE_RDTSC

Commit-ID:  0bf17c102177d5da9363bf8b1e4704b9996d5079
Gitweb:     https://git.kernel.org/tip/0bf17c102177d5da9363bf8b1e4704b9996d5079
Author:     Tom Lendacky <thomas.lendacky@....com>
AuthorDate: Fri, 5 Jan 2018 10:07:56 -0600
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Sat, 6 Jan 2018 21:57:40 +0100

x86/cpu/AMD: Use LFENCE_RDTSC instead of MFENCE_RDTSC

With LFENCE now a serializing instruction, set the LFENCE_RDTSC
feature since the LFENCE instruction has less overhead than the
MFENCE instruction.

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Borislav Petkov <bp@...en8.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...ux-foundation.org>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: Paul Turner <pjt@...gle.com>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20180105160756.23786.4220.stgit@tlendack-t1.amdoffice.net

---
 arch/x86/kernel/cpu/amd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index fbd439e..b221fe5 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -838,8 +838,8 @@ static void init_amd(struct cpuinfo_x86 *c)
 		msr_set_bit(MSR_F10H_DECFG,
 			    MSR_F10H_DECFG_LFENCE_SERIALIZE_BIT);
 
-		/* MFENCE stops RDTSC speculation */
-		set_cpu_cap(c, X86_FEATURE_MFENCE_RDTSC);
+		/* A serializing LFENCE stops RDTSC speculation */
+		set_cpu_cap(c, X86_FEATURE_LFENCE_RDTSC);
 	}
 
 	/*