linux-kernel - Re: [PATCH RFC 2/5] x86/speculation: Add support for 'cpu_spec

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Message-ID: <20190405160536.sks2hmo6sxnxg3tl@treble>
Date:   Fri, 5 Apr 2019 11:05:36 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Kosina <jikos@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jon Masters <jcm@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        linux-s390@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tyler Hicks <tyhicks@...onical.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH RFC 2/5] x86/speculation: Add support for
 'cpu_spec_mitigations=' cmdline options

On Fri, Apr 05, 2019 at 05:26:50PM +0200, Borislav Petkov wrote:
> On Fri, Apr 05, 2019 at 09:31:01AM -0500, Josh Poimboeuf wrote:
> > My thinking was that the individual options could be used to override
> > the global option.  But maybe that's overkill?  I dunno.
> 
> You mean if the user deliberately types:
> 
> "cpu_spec_mitigations=off spectre_v2=auto"
> 
> on the cmdline to turn off all and then enable only one?
> 
> Hmm, yap, sounds like an overkill to me. Then I'd probably do:
> 
> 	pr_err("Make up your mind already!\n");
> 	return;
> 
> :-))
> 
> I'd say let's do the simpler and cleaner thing now and think about
> supporting this overkill when it really turns out that it is needed.

Fair enough.

> > I assume you mean just the part where L1TF_MITIGATION_DEFAULT is added?
> 
> Yap.

Ok.

-- 
Josh