From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DFC2EC43387 for ; Mon, 31 Dec 2018 07:20:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AE0DB21019 for ; Mon, 31 Dec 2018 07:20:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727062AbeLaHUh (ORCPT ); Mon, 31 Dec 2018 02:20:37 -0500 Received: from ex13-edg-ou-002.vmware.com ([208.91.0.190]:25217 "EHLO EX13-EDG-OU-002.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726381AbeLaHUh (ORCPT ); Mon, 31 Dec 2018 02:20:37 -0500 Received: from sc9-mailhost3.vmware.com (10.113.161.73) by EX13-EDG-OU-002.vmware.com (10.113.208.156) with Microsoft SMTP Server id 15.0.1156.6; Sun, 30 Dec 2018 23:20:33 -0800 Received: from sc2-haas01-esx0118.eng.vmware.com (sc2-haas01-esx0118.eng.vmware.com [10.172.44.118]) by sc9-mailhost3.vmware.com (Postfix) with ESMTP id 75C4940687; Sun, 30 Dec 2018 23:20:35 -0800 (PST) From: Nadav Amit To: Ingo Molnar , Andy Lutomirski , Peter Zijlstra , Josh Poimboeuf , Edward Cree CC: "H . Peter Anvin" , Thomas Gleixner , LKML , Nadav Amit , X86 ML , Paolo Abeni , Borislav Petkov , David Woodhouse , Nadav Amit Subject: [RFC v2 0/6] x86: dynamic indirect branch promotion Date: Sun, 30 Dec 2018 23:21:06 -0800 Message-ID: <20181231072112.21051-1-namit@vmware.com> X-Mailer: git-send-email 2.17.1 MIME-Version: 1.0 Content-Type: text/plain Received-SPF: None (EX13-EDG-OU-002.vmware.com: namit@vmware.com does not designate permitted sender hosts) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a revised version of optpolines (formerly named retpolines) for dynamic indirect branch promotion in order to reduce retpoline overheads [1]. This version address some of the concerns that were raised before. Accordingly, the code was slightly simplified and patching is now done using the regular int3/breakpoint mechanism. Outline optpolines for multiple targets was added. I do not think the way I implemented it is the correct one. In my original (private) version, if there are more targets than the outline block can hold, the outline block is completely removed. However, I think this is more-or-less how Josh wanted it to be. The code modifications are now done using a gcc-plugin. This allows to easily ignore code from init and other code sections. I think it should also allow us to add opt-in/opt-out support for each branch, for example by marking function pointers using address-space attributes. All of these changes required some optimizations to go away to keep the code simple. I have still did not run the benchmarks again. So I might have not addressed all the open issues, but it is rather hard to finish the implementation since some still open high-level decisions affect the way in which optimizations should be done. Specifically: - Is it going to be the only indirect branch promotion mechanism? If so, it probably should also provide interface similar to Josh's "static-calls" with annotations. - Should it also be used when retpolines are disabled (in the config)? This does complicate the implementation a bit (RFC v1 supported it). - Is it going to be opt-in or opt-out? If it is an opt-out mechanism, memory and performance optimizations need to be more aggressive. - Do we use periodic learning or not? Josh suggested to reconfigure the branches whenever a new target is found. However, I do not know at this time how to do learning efficiently, without making learning much more expensive. [1] https://lore.kernel.org/patchwork/cover/1001332/ Nadav Amit (6): x86: introduce kernel restartable sequence objtool: ignore instructions x86: patch indirect branch promotion x86: interface for accessing indirect branch locations x86: learning and patching indirect branch targets x86: outline optpoline arch/x86/Kconfig | 4 + arch/x86/entry/entry_64.S | 16 +- arch/x86/include/asm/nospec-branch.h | 83 ++ arch/x86/include/asm/sections.h | 2 + arch/x86/kernel/Makefile | 1 + arch/x86/kernel/asm-offsets.c | 9 + arch/x86/kernel/nospec-branch.c | 1293 ++++++++++++++++++ arch/x86/kernel/traps.c | 7 + arch/x86/kernel/vmlinux.lds.S | 7 + arch/x86/lib/retpoline.S | 83 ++ include/linux/cpuhotplug.h | 1 + include/linux/module.h | 9 + kernel/module.c | 8 + scripts/Makefile.gcc-plugins | 3 + scripts/gcc-plugins/x86_call_markup_plugin.c | 329 +++++ tools/objtool/check.c | 21 +- 16 files changed, 1872 insertions(+), 4 deletions(-) create mode 100644 arch/x86/kernel/nospec-branch.c create mode 100644 scripts/gcc-plugins/x86_call_markup_plugin.c -- 2.17.1