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

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Date:   Fri, 5 Jan 2018 17:56:01 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        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: Re: [PATCH v1 0/3] x86/cpu/AMD: Make LFENCE a serializing
 instruction on AMD

On Fri, Jan 05, 2018 at 10:07:36AM -0600, Tom Lendacky wrote:
> 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

All three:

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

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