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

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Date:   Thu, 4 Jan 2018 11:02:31 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Andrea Arcangeli <aarcange@...hat.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 01/04/2018 10:34 AM, Andrea Arcangeli wrote:
> 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
> 

Yes, will correct.

Thanks.