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

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Message-ID: <20180104183435.GK13348@redhat.com>
Date:   Thu, 4 Jan 2018 19:34:35 +0100
From:   Andrea Arcangeli <aarcange@...hat.com>
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>,
        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 09:56:47AM -0800, Tim Chen wrote:
> There are 2 ways to control IBRS
> 
> 1. At boot time
>     noibrs kernel boot parameter will disable IBRS usage
> 
> Otherwise if the above parameters are not specified, the system
> will enable ibrs and ibpb usage if the cpu supports it.
> 
> 2. At run time
>     echo 0 > /sys/kernel/debug/ibrs_enabled will turn off IBRS
>     echo 1 > /sys/kernel/debug/ibrs_enabled will turn on IBRS in kernel
>     echo 2 > /sys/kernel/debug/ibrs_enabled will turn on IBRS in both userspace and kernel

debug/x86/?

Reviewed-by: Andrea Arcangeli <aarcange@...hat.com>

Thanks,
Andrea