linux-kernel - Re: [PATCH 6/7] x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC

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Message-ID: <20180104185514.spfj4novp5sbud3r@pd.tnic>
Date:   Thu, 4 Jan 2018 19:55:14 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] x86/spec_ctrl: Add sysctl knobs to enable/disable
 SPEC_CTRL feature

On Thu, Jan 04, 2018 at 07:38:26PM +0100, Andrea Arcangeli wrote:
> Consolidating in arch/x86/kernel/spec_ctrl.c would allow removing that
> export.
> 
> Here I've got:
> 
> static DEFINE_MUTEX(spec_ctrl_mutex);

Yap.

> Turning this off at any time is very easy, making reptoline runtime
> disabled is more difficult.

So dwmw2 is doing alternatives. Seems workable to me.

Also, you don't want to slap all those different settings in front of
the user and then expect her to do an informed choice in all cases.

So it should be a very simple first set of choices what to set and then
add more only when really needed and when it really makes sense.

IMO.

-- 
Regards/Gruss,
    Boris.

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