linux-kernel - Is: Linus, name for 'spectre' variable. Was:Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC

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Date:   Sat, 6 Jan 2018 16:46:18 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>,
        Konrad Rzeszutek Wilk <konrad@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Is: Linus, name for 'spectre' variable. Was:Re: [PATCH v2 4/8]
 x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC_CTRL feature

On Sat, Jan 06, 2018 at 10:39:27PM +0100, Thomas Gleixner wrote:
> On Sat, 6 Jan 2018, Konrad Rzeszutek Wilk wrote:
> > On Sat, Jan 06, 2018 at 08:47:19PM +0100, Thomas Gleixner wrote:
> > > On Sat, 6 Jan 2018, Dave Hansen wrote:
> > > 
> > > > On 01/06/2018 09:41 AM, Van De Ven, Arjan wrote:
> > > > >>>>  .macro DISABLE_IBRS
> > > > >>>> -	ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_SPEC_CTRL
> > > > >>>> +	testl	$1, dynamic_ibrs
> > > > >>> On every system call we end up hammering on this 'dynamic_ibrs'
> > > > >>> variable. And it looks like it can be flipped via the IPI mechanism.
> > > > >>>
> > > > >>> Would it make sense for this to be per-cpu?
> > > > >>
> > > > >> It's probably better to either just make it __read_mostly or get the
> > > > >> static branches that folks were suggesting actually working.
> > > > > 
> > > > > I still wonder if this isn't just better as a boot command line
> > > > 
> > > > It's simpler that way.  But, ideally, we want to make it runtime
> > > > switchable to match the implementation in the distros.
> > > 
> > > Stop this silly argument please. The distros shipped lots of crap which we
> > > dont want to have at all.
> > > 
> > > I told you folks yesterday what I want to see and the sysctl thing is the
> > > least on that list and it's not needed for getting the important thing -
> > > the protection - to work.
> > 
> > I agree. But this is what customers are told to inspect to see if they
> > are impacted. And if in the future versions this goes away or such - they
> > will freak out and cause needless escalations.
> 
> That's the result of distros cramming stuff into their kernels without
> talking to us. It's their problem to explain that their customers.

I am trying to resolve this now for those distros's that haven't
crammed these patches in yet and get a resolution on the naming _now_
so they can update it to have the right name from the gecko for the future.

Lets rope in the boss.

> 
> We can talks about the sysctl _AFTER_ fixing the real issues.

Perhaps we can delegate this to Linus.
> 
> Thanks,
> 
> 	tglx