linux-kernel - Re: [PATCH v2] x86/speculation: Add support for STIBP always-on preferred mode

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Date:   Wed, 12 Dec 2018 10:59:38 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jiri Kosina <jkosina@...e.cz>, Ingo Molnar <mingo@...hat.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [PATCH v2] x86/speculation: Add support for STIBP always-on
 preferred mode

On Tue, Dec 11, 2018 at 07:37:26PM -0800, Thomas Gleixner wrote:
> Hmmm. I've not seen the V1 of this (it's not in my inbox) but the v1->v2
> changes contain:

You're on CC:

https://lkml.kernel.org/r/20181211190959.28321.56433.stgit@tlendack-t1.amdoffice.net

> 
> > > - Removed explicit SPECTRE_V2_USER_STRICT_PREFERRED mode
> 
> Now I really have to ask why?
> 
> Neither the extra variable nor the cpu feature check are pretty. An
> explicit mode is way better in terms of code clarity and you get the proper
> printout via spectre_v2_user_strings.

Actually, now that I've slept on it, I think we should do this just
like X86_FEATURE_IBRS_ENHANCED - as a modifier for SPECTRE_V2_CMD_AUTO
or _FORCE options.

And that has its own mode SPECTRE_V2_IBRS_ENHANCED.

Makes sense?

-- 
Regards/Gruss,
    Boris.

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