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

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Message-ID: <20180123224956.GQ7844@tassilo.jf.intel.com>
Date:   Tue, 23 Jan 2018 14:49:56 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     "Woodhouse, David" <dwmw@...zon.co.uk>,
        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

> 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.

-Andi