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Message-ID: <1516749276.13558.25.camel@amazon.co.uk>
Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation
To:     Andi Kleen <ak@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>
CC:     Andy Lutomirski <luto@amacapital.net>,
        KarimAllah Ahmed <karahmed@amazon.de>,
        <linux-kernel@vger.kernel.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Borislav Petkov <bp@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>,
        Joerg Roedel <joro@8bytes.org>,
        "Jun Nakajima" <jun.nakajima@intel.com>,
        Laura Abbott <labbott@redhat.com>,
        "Linus Torvalds" <torvalds@linux-foundation.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@linux.intel.com>, <kvm@vger.kernel.org>,
        <x86@kernel.org>, "Arjan Van De Ven" <arjan.van.de.ven@intel.com>
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Content-Type: multipart/signed; micalg=sha-256; protocol="application/x-pkcs7-signature"; boundary="=-q+mZOhcj9cJaZ9CQ8Sfx"
Date:   Tue, 23 Jan 2018 23:14:36 +0000
MIME-Version: 1.0
From:   "Woodhouse, David" <dwmw@amazon.co.uk>
Sender: linux-kernel-owner@vger.kernel.org
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Content-Type: text/plain; charset="UTF-8"
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On Tue, 2018-01-23 at 14:49 -0800, Andi Kleen wrote:
> > Not sure.=C2=A0 Maybe to start, the answer might be to allow it to be s=
et for
> > the ultra-paranoid, but in general don't enable it by default.=C2=A0 Ha=
ving it
> > enabled would be an alternative to someone deciding to disable SMT, sin=
ce
> > that would have even more of a performance impact.
>=20
> 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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