linux-kernel - Re: [PATCH v5 2/2] x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation

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Message-ID: <f95c28d6-70f2-3f18-4ab9-c756c7581126@amd.com>
Date:   Wed, 12 Sep 2018 12:16:16 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Jiri Kosina <jikos@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        "Schaufler, Casey" <casey.schaufler@...el.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v5 2/2] x86/speculation: Enable cross-hyperthread spectre
 v2 STIBP mitigation



On 09/11/2018 04:16 PM, Thomas Gleixner wrote:
> On Tue, 11 Sep 2018, Tim Chen wrote:
>> On 09/10/2018 04:46 AM, Jiri Kosina wrote:
>>> Nah, IBPB is actuall there, sorry. So I'll add reporting of STIBP + fixup 
>>> the missing reporting of RSB_CTXSW for v6.
>>>
>>
>> I anticipate that STIBP could affect workloads with a lot of indirect
>> branches (see previous discussion with Andrea).  We should have a 
>> knob for people to opt in or opt out of STIBP.
> 
> Feel free to send a patch to that effect.

Tim, are you planning on sending a patch for this?  If so, what type of
opt in/out are you thinking about, something similar to SSBD?

Thanks,
Tom

> 
> Thanks,
> 
> 	tglx
>