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

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Date:   Wed, 12 Dec 2018 14:04:35 +0000
From:   "Lendacky, Thomas" <Thomas.Lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     "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 12/12/2018 03:59 AM, Borislav Petkov wrote:
> 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?

Not sure I completely follow. Are you saying to do what I did in my
first patch or something different from that yet?

Thanks,
Tom

>