Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933580AbeAOKNi (ORCPT + 1 other); Mon, 15 Jan 2018 05:13:38 -0500 Received: from twosheds.infradead.org ([90.155.92.209]:34908 "EHLO twosheds.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933379AbeAOKNe (ORCPT ); Mon, 15 Jan 2018 05:13:34 -0500 Message-ID: <1516011195.22147.132.camel@infradead.org> Subject: Re: [tip:x86/pti] x86/retpoline: Fill RSB on context switch for affected CPUs From: David Woodhouse To: Andi Kleen , pjt@google.com, linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com, riel@redhat.com, jikos@kernel.org, jpoimboe@redhat.com, luto@amacapital.net, torvalds@linux-foundation.org, tglx@linutronix.de, hpa@zytor.com, peterz@infradead.org, dave.hansen@intel.com, mingo@kernel.org, keescook@google.com, gregkh@linux-foundation.org, arjan@linux.intel.com Cc: linux-tip-commits@vger.kernel.org In-Reply-To: <20180115000554.GA7844@tassilo.jf.intel.com> References: <1515779365-9032-1-git-send-email-dwmw@amazon.co.uk> <20180115000554.GA7844@tassilo.jf.intel.com> Face: 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 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-9mUKiHnrSfvYvt7XIAmP" Date: Mon, 15 Jan 2018 11:13:16 +0100 Mime-Version: 1.0 X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 X-SRS-Rewrite: SMTP reverse-path rewritten from by twosheds.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: --=-9mUKiHnrSfvYvt7XIAmP Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2018-01-14 at 16:05 -0800, Andi Kleen wrote: > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if ((!boot_cpu_has(X86_FEATURE_PTI) && > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 !boot_cpu_has(X= 86_FEATURE_SMEP)) || is_skylake_era()) { > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW); > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0pr_info("Filling RSB on context switch\n"); > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0} >=20 > Missing an option to turn this off. Deliberately so. You can already boot with 'spectre_v2=3Doff' to turn off the mitigations. We are not intending to permit all the bullshit micro- management of IBRS=3D3/IBPB=3D2/RSB=3D=CF=80 nonsense. If you choose retpoline, you get the RSB stuffing which is appropriate along with that. With IBRS, you get the RSB stuffing which is appropriate with that. You don't get command line or sysfs tunables to mess it. You *do* have the source code, if you really want to make changes. 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