Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 23 Jan 2018 15:22:35 -0800
From:   Andi Kleen <ak@linux.intel.com>
To:     "Woodhouse, David" <dwmw@amazon.co.uk>
Cc:     "thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "ashok.raj@intel.com" <ashok.raj@intel.com>,
        "Raslan, KarimAllah" <karahmed@amazon.de>,
        "arjan.van.de.ven@intel.com" <arjan.van.de.ven@intel.com>,
        "arjan@linux.intel.com" <arjan@linux.intel.com>,
        "bp@suse.de" <bp@suse.de>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "Janakarajan.Natarajan@amd.com" <Janakarajan.Natarajan@amd.com>,
        "tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>,
        "torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
        "joro@8bytes.org" <joro@8bytes.org>,
        "dan.j.williams@intel.com" <dan.j.williams@intel.com>,
        "x86@kernel.org" <x86@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>,
        "aarcange@redhat.com" <aarcange@redhat.com>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "luto@kernel.org" <luto@kernel.org>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "dave.hansen@intel.com" <dave.hansen@intel.com>,
        "luto@amacapital.net" <luto@amacapital.net>,
        "mhiramat@kernel.org" <mhiramat@kernel.org>,
        "asit.k.mallick@intel.com" <asit.k.mallick@intel.com>,
        "jun.nakajima@intel.com" <jun.nakajima@intel.com>,
        "labbott@redhat.com" <labbott@redhat.com>,
        "rkrcmar@redhat.com" <rkrcmar@redhat.com>
Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation
Message-ID: <20180123232235.GT7844@tassilo.jf.intel.com>
References: <1516476182-5153-1-git-send-email-karahmed@amazon.de>
 <1516476182-5153-10-git-send-email-karahmed@amazon.de>
 <243BE571-AF73-44B3-8D17-193F9E07686A@amacapital.net>
 <4e01a7a9-29e4-adcc-3f53-550fb7f3d370@amd.com>
 <1516724457.9521.156.camel@amazon.co.uk>
 <fb2b5589-e14c-470e-2de0-d9da1667bace@amd.com>
 <20180123224956.GQ7844@tassilo.jf.intel.com>
 <1516749276.13558.25.camel@amazon.co.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <1516749276.13558.25.camel@amazon.co.uk>
User-Agent: Mutt/1.9.1 (2017-09-22)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Jan 23, 2018 at 11:14:36PM +0000, Woodhouse, David wrote:
> 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?

Right.

-Andi