linux-kernel - Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC

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Date:   Mon, 8 Jan 2018 16:08:00 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     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>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable
 SPEC_CTRL feature

On Fri, Jan 05, 2018 at 06:12:19PM -0800, Tim Chen wrote:
> +void scan_spec_ctrl_feature(struct cpuinfo_x86 *c)
> +{
> +	if ((!c->cpu_index) && (boot_cpu_has(X86_FEATURE_SPEC_CTRL))) {

We should test X86_BUG_SPECTRE_V1 here too before default enabling this,
no?

> +		if (!ibrs_admin_disabled) {
> +			dynamic_ibrs = 1;
> +			ibrs_enabled = IBRS_ENABLED;
> +		}
> +	}
> +}