linux-kernel - Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation

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Message-ID: <1516749276.13558.25.camel@amazon.co.uk>
Date:   Tue, 23 Jan 2018 23:14:36 +0000
From:   "Woodhouse, David" <dwmw@...zon.co.uk>
To:     Andi Kleen <ak@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>
CC:     Andy Lutomirski <luto@...capital.net>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        <linux-kernel@...r.kernel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Joerg Roedel <joro@...tes.org>,
        "Jun Nakajima" <jun.nakajima@...el.com>,
        Laura Abbott <labbott@...hat.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>, <kvm@...r.kernel.org>,
        <x86@...nel.org>, "Arjan Van De Ven" <arjan.van.de.ven@...el.com>
Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation

On Tue, 2018-01-23 at 14:49 -0800, Andi Kleen wrote:
> > Not sure.  Maybe to start, the answer might be to allow it to be set for
> > the ultra-paranoid, but in general don't enable it by default.  Having it
> > enabled would be an alternative to someone deciding to disable SMT, since
> > that would have even more of a performance impact.
> 
> I agree. A reasonable strategy would be to only enable it for
> processes that have dumpable disabled. This should be already set for
> high value processes like GPG, and allows others to opt-in if
> they need to.

That seems to make sense, and I think was the solution we were
approaching for IBPB on context switch too, right?

Are we generally agreed on dumpable as the criterion for both of those?
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