linux-kernel - Re: [PATCH] x86/speculation: Add document to describe Spectre and its mitigations

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Date:   Mon, 31 Dec 2018 08:22:39 -0800
From:   Ben Greear <greearb@...delatech.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jon Masters <jcm@...hat.com>,
        Waiman Long <longman9394@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        x86@...nel.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/speculation: Add document to describe Spectre and its
 mitigations



On 12/21/2018 05:17 PM, Tim Chen wrote:
> On 12/21/18 1:59 PM, Ben Greear wrote:
>> On 12/21/18 9:44 AM, Tim Chen wrote:
>>> Thomas,
>>>
>>> Andi and I have made an update to our draft of the Spectre admin guide.
>>> We may be out on Christmas vacation for a while.  But we want to
>>> send it out for everyone to take a look.
>>
>> Can you add a section on how to compile out all mitigations that have anything
>> beyond negligible performance impact for those running systems where performance
>> is more important than security?
>>
>
> If you don't worry about security and performance is paramount, then
> boot with "nospectre_v2".  That's explained in the document.

There seem to be lots of different variants of this type of problem.  It was not clear
to me that just doing nospectre_v2 would be sufficient to get back full performance.

And anyway, I would like to compile the kernel to not need that command-line option,
so I am still interesting in what compile options need to be set to what values...

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com