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Subject: Re: [PATCH] x86/speculation: Add document to describe Spectre and its
 mitigations
To:     Tim Chen <tim.c.chen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>
References: <64efec3fda40c0758601bf9b1480a35d76d3c487.1545413988.git.tim.c.chen@linux.intel.com>
 <1c7923ec-70aa-25d4-3de1-f1b1768bb80b@candelatech.com>
 <fdf4e1cd-9b28-75c7-6846-6d0f5b816936@linux.intel.com>
Cc:     Jiri Kosina <jikos@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Andi Kleen <ak@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Jon Masters <jcm@redhat.com>,
        Waiman Long <longman9394@gmail.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Borislav Petkov <bp@alien8.de>, linux-kernel@vger.kernel.org,
        x86@kernel.org, stable@vger.kernel.org
From:   Ben Greear <greearb@candelatech.com>
Message-ID: <5d45f3ef-a91f-815a-f532-62e75899e697@candelatech.com>
Date:   Mon, 31 Dec 2018 08:22:39 -0800
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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@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com