linux-kernel - Re: [PATCH v1 1/3] x86/cpu/AMD: Make LFENCE a serializing instruction

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Message-ID: <29225f25-033b-92d5-2e19-29eb557665d6@amd.com>
Date:   Fri, 5 Jan 2018 10:36:40 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Brian Gerst <brgerst@...il.com>
Cc:     the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        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: Re: [PATCH v1 1/3] x86/cpu/AMD: Make LFENCE a serializing instruction

On 1/5/2018 10:35 AM, Brian Gerst wrote:
> On Fri, Jan 5, 2018 at 11:07 AM, Tom Lendacky <thomas.lendacky@....com> wrote:
>> To aid in speculation control, make LFENCE a serializing instruction.
>> This is done by setting bit 1 of MSR 0xc0011029 (DE_CFG).  Some families
>> that support LFENCE do not have this MSR.  For these families, the LFENCE
>> instruction is already serializing.
> 
> Does this require a microcode update?

No, it doesn't.

Thanks,
Tom

> 
> --
> Brian Gerst
>