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

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Date:   Wed, 12 Dec 2018 15:04:07 +0000
From:   "Lendacky, Thomas" <Thomas.Lendacky@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Borislav Petkov <bp@...en8.de>, "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 08:23 AM, Thomas Gleixner wrote:
> On Wed, 12 Dec 2018, Lendacky, Thomas wrote:
>> On 12/11/2018 09:37 PM, Thomas Gleixner wrote:
>>> On Wed, 12 Dec 2018, Borislav Petkov wrote:
>>>> I still don't like that separate stibp_always_on variable when we can do
>>>> all the querying just by using mode and X86_FEATURE_AMD_STIBP_ALWAYS_ON.
>>>
>>> Hmmm. I've not seen the V1 of this (it's not in my inbox) but the v1->v2
>>> changes contain:
>>
>> That's strange, you were on the cc: list. Anyway, here's a link to the
>> first version: https://lkml.org/lkml/2018/12/11/1248
> 
> Must have been my sleep deprived brain. Found it now :) Sorry for not
> paying attention back then.
> 
>>>>> - 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.
>>>
>>> Hmm?
>>
>> That is what the first version did. See if that's in-line with what
>> you're thinking.
> 
> Yes, though I'm not too fond about the preferred wording, but can't come up
> with anything better.

I'm not crazy about that either. Maybe getting rid of "preferred" and just
having "always-on" for the wording is enough?

Thanks,
Tom

> 
> Thanks,
> 
> 	tglx
>