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

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Date:   Mon, 19 Nov 2018 14:44:24 -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 12:21 PM, Thomas Gleixner wrote:
> On Fri, 16 Nov 2018, Tim Chen wrote:
>> +static enum spectre_v2_app2app_mitigation_cmd __init
>> +	    spectre_v2_parse_app2app_cmdline(enum spectre_v2_mitigation_cmd v2_cmd)
>> +{
>> +	enum spectre_v2_app2app_mitigation_cmd cmd;
>> +	char arg[20];
>> +	int ret, i;
>> +
>> +	if (v2_cmd == SPECTRE_V2_CMD_FORCE) {
>> +		cmd = SPECTRE_V2_APP2APP_CMD_FORCE;
>> +		goto show_cmd;
> 
> What initializes 'i' in this case? Compiler warnings are overrated.

Will fix.

> 
> What exactly handles the SPECTRE_V2_NONE case which you documented in the
> commandline bits?
> 

The default spectre_v2_app2app_enabled is set to SPECTRE_V2_APP2APP_NONE.

When we have SPECTRE_V2_NONE case, we will have return in spectre_v2_select_mitigation
without calling spectre_v2_parse_app2app_cmdline. So we will have
SPECTRE_V2_APP2APP_NONE.

Tim