linux-kernel - Re: [tip:x86/pti] x86/retpoline: Fill RSB on context switch for affected CPUs

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Message-ID: <20180115000904.GA10203@tassilo.jf.intel.com>
Date:   Sun, 14 Jan 2018 16:09:04 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     pjt@...gle.com, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com, riel@...hat.com, jikos@...nel.org,
        jpoimboe@...hat.com, luto@...capital.net,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        dwmw@...zon.co.uk, hpa@...or.com, peterz@...radead.org,
        dave.hansen@...el.com, mingo@...nel.org, keescook@...gle.com,
        gregkh@...ux-foundation.org, arjan@...ux.intel.com
Cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/pti] x86/retpoline: Fill RSB on context switch for
 affected CPUs

On Sun, Jan 14, 2018 at 04:05:54PM -0800, Andi Kleen wrote:
> > +	if ((!boot_cpu_has(X86_FEATURE_PTI) &&
> > +	     !boot_cpu_has(X86_FEATURE_SMEP)) || is_skylake_era()) {
> > +		setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
> > +		pr_info("Filling RSB on context switch\n");
> > +	}
> 
> Missing an option to turn this off.

My earlier patch did this properly by folding it 
into the big option parser.

https://marc.info/?l=linux-kernel&m=151578282016915&w=2

-Andi