linux-kernel - [PATCH v1 0/3] x86/cpu/AMD: Make LFENCE a serializing instruction on AMD

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Message-ID: <20180105160736.23786.45026.stgit@tlendack-t1.amdoffice.net>
Date:   Fri, 05 Jan 2018 10:07:36 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Paul Turner <pjt@...gle.com>
Subject: [PATCH v1 0/3] x86/cpu/AMD: Make LFENCE a serializing instruction
 on AMD

To aid in speculation control, the LFENCE instruction will be turned into
a serializing instruction. There is less performance impact using LFENCE
in this way compared to MFENCE.

With LFENCE now being a serializing instruction, it can be used in
rdtsc_ordered() in place of MFENCE_RDTSC.  The other two patches in this
series make this change and remove the MFENCE_RDTSC feature.

The following patches are included in this series:
- Make LFENCE a serializing instruction on AMD
- Change over to LFENCE_RDTSC from MFENCE_RDTSC on AMD
- Remove the MFENCE_RDTSC feature

This patch series is based on tip:x86/pti.

---

Tom Lendacky (3):
      x86/cpu/AMD: Make LFENCE a serializing instruction
      x86/cpu/AMD: Use LFENCE_RDTSC instead of MFENCE_RDTSC
      x86/msr: Remove now unused definition of MFENCE_RDTSC feature


 arch/x86/include/asm/cpufeatures.h |    2 +-
 arch/x86/include/asm/msr-index.h   |    2 ++
 arch/x86/include/asm/msr.h         |    3 +--
 arch/x86/kernel/cpu/amd.c          |   13 +++++++++++--
 4 files changed, 15 insertions(+), 5 deletions(-)

-- 
Tom Lendacky