linux-kernel - Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app protection modes

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Message-ID: <d4b538ba-ce4f-978c-8ccf-cf89187f265a@linux.intel.com>
Date:   Mon, 19 Nov 2018 10:27:38 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jiri Kosina <jikos@...nel.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>,
        Casey Schaufler <casey.schaufler@...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>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app
 protection modes

On 11/19/2018 07:00 AM, Thomas Gleixner wrote:
> On Fri, 16 Nov 2018, Tim Chen wrote:
>> +DEFINE_STATIC_KEY_FALSE(spectre_v2_app_lite);
>> +EXPORT_SYMBOL_GPL(spectre_v2_app_lite);
> 
> Why would this be exported? The only usage site outside of this code is in
> tlb.c which is hardly modular.

That was my initial thought too.  Ingo suggested to export it in
review of v2.  Wonder Ingo has some reason?

https://lore.kernel.org/patchwork/patch/991759/

> 
>> @@ -328,14 +411,19 @@ static bool stibp_needed(void)
>>  	/*
>>  	 * Determine if STIBP should be always on.
>>  	 * Using enhanced IBRS makes using STIBP unnecessary.
>> +	 * For lite option, STIBP is used only for task with
>> +	 * TIF_STIBP flag. STIBP is not always on for that case.
> 
> Having the comment detached from the code is really not helpful.
> 

Sorry, would have the comment moved.

Tim