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 10:31:27 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Jiri Kosina <jikos@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     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>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Willy Tarreau <w@....eu>
Subject: Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app
 protection modes

On 11/19/2018 06:00 AM, Jiri Kosina wrote:
> On Mon, 19 Nov 2018, Thomas Gleixner wrote:
> 
>>> Yeah. IBPB implementation used to check the dumpability of tasks during 
>>> rescheduling, but that went away later.
>>>
>>> I still think that ideally that 'app2app' setting would toggle how IBPB is 
>>> being used as well, something along the lines:
>>>
>>> lite:
>>> 	- STIBP for the ones marked via prctl() and SECCOMP with the TIF_ 
>>> 	  flag
>>> 	- ibpb_needed() returning true for the same
>>>
>>> strict:
>>> 	- STIBP: as currently implemented
>>> 	- ibpb_needed() returning always true
>>>
>>> off:
>>> 	- neither STIBP nor IBPB applied ever
>>>
>>> That's give us also some % of performance lost via IBPB back.
>>>
>>> Makes sense?
>>
>> Except for the naming convention, yes. See other mail.
> 
> Actually Tim's patchset seems to already deal with IBPB in a consistent 
> way as well in
> 
> 	[11/16] x86/speculation: Add Spectre v2 app to app protection modes
> 
> but the fact that it's still using TIF_STIBP makes it a bit confusing and 
> hidden. So I'd suggest to fold something like below into it.
> 

Makes sense.  Will rename the flag.

Tim