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=-6.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=no 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 452B0C388F9 for ; Sun, 8 Nov 2020 04:29:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0A4F320760 for ; Sun, 8 Nov 2020 04:29:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726455AbgKHE3j (ORCPT ); Sat, 7 Nov 2020 23:29:39 -0500 Received: from mga14.intel.com ([192.55.52.115]:27415 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726062AbgKHE3j (ORCPT ); Sat, 7 Nov 2020 23:29:39 -0500 IronPort-SDR: 8a9XPfdkU4TwCwEoCkUK8x7Zuwubcv+FJ9eLPVfKw2EvZXrKrX9R7hLqPlZC2NZ2dSySXld0NR joW1qsC42tGQ== X-IronPort-AV: E=McAfee;i="6000,8403,9798"; a="168900972" X-IronPort-AV: E=Sophos;i="5.77,460,1596524400"; d="scan'208";a="168900972" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Nov 2020 20:29:38 -0800 IronPort-SDR: IusSYOOlqv26m8r5wxSymQmNKik71JEglBymRRS9PgMEgN6iHzAws2wB8fBTRtu01OodJ4JHyN HcKw2/WlHBhw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.77,460,1596524400"; d="scan'208";a="307244978" Received: from otcwcpicx6.sc.intel.com ([172.25.55.29]) by fmsmga008.fm.intel.com with ESMTP; 07 Nov 2020 20:29:38 -0800 From: Fenghua Yu To: "Borislav Petkov" , "Thomas Gleixner" , "Ingo Molnar" , "Peter Zijlstra" , "Tony Luck" , "Randy Dunlap" , "Xiaoyao Li " , "Ravi V Shankar" Cc: "linux-kernel" , "x86" , Fenghua Yu Subject: [PATCH 0/4] x86/bus_lock: Enable bus lock detection Date: Sun, 8 Nov 2020 04:29:14 +0000 Message-Id: <20201108042918.1011889-1-fenghua.yu@intel.com> X-Mailer: git-send-email 2.29.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A bus lock [1] is acquired either through split locked access to writeback (WB) memory or by using locks to uncacheable (UC) memory (e.g. direct device assignment). This is typically >1000 cycles slower than an atomic operation within a cache line. It also disrupts performance on other cores. Although split lock can be detected by #AC trap, the trap is triggered before the instruction acquires bus lock. This makes it difficult to mitigate bus lock (e.g. throttle the user application). Some CPUs have ability to notify the kernel by an #DB trap after a user instruction acquires a bus lock and is executed. This allows the kernel to enforce user application throttling or mitigations. #DB for bus lock detect fixes issues in #AC for split lock detect: 1) It's architectural ... just need to look at one CPUID bit to know it exists 2) The IA32_DEBUGCTL MSR, which reports bus lock in #DB, is per-thread. So each process or guest can have different behavior. 3) It has support for VMM/guests (new VMEXIT codes, etc). Hardware only generates #DB for bus lock detect when CPL>0 to avoid nested #DB from multiple bus locks while the first #DB is being handled. Use the existing kernel command line option "split_lock_detect=" to handle #DB for bus lock: split_lock_detect= #AC for split lock #DB for bus lock off Do nothing Do nothing warn Kernel OOPs Warn once per task and Warn once per task and and continues to run. disable future checking When both features are supported, warn in #DB fatal Kernel OOPs Send SIGBUS to user Send SIGBUS to user When both features are supported, fatal in #AC. ratelimit:N Do nothing Limit bus lock rate to N per second in the current non-root user. Default split_lock_detect is "warn". [1] Intel Instruction Set Extension Chapter 8: https://software.intel.com/sites/default/files/managed/c5/15/architecture-instruction-set-extensions-programming-reference.pdf Change Log: - Check bus lock bit by its positive polarity (Xiaoyao). - Fix a few wording issues in the documentation (Randy). [RFC v3 can be found at: https://lore.kernel.org/patchwork/cover/1329943/] RFC v3: - Remove DR6_RESERVED change (PeterZ). - Simplify the documentation (Randy). RFC v2: - Architecture changed based on feedback from Thomas and PeterZ. #DB is no longer generated for bus lock in ring0. - Split the one single patch into four patches. [RFC v1 can be found at: https://lore.kernel.org/lkml/1595021700-68460-1-git-send-email-fenghua.yu@intel.com/] Fenghua Yu (4): x86/cpufeatures: Enumerate #DB for bus lock detection x86/bus_lock: Handle warn and fatal in #DB for bus lock x86/bus_lock: Set rate limit for bus lock Documentation/admin-guide: Change doc for split_lock_detect parameter .../admin-guide/kernel-parameters.txt | 30 +++- arch/x86/include/asm/cpu.h | 9 +- arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/include/asm/msr-index.h | 1 + arch/x86/include/uapi/asm/debugreg.h | 1 + arch/x86/kernel/cpu/common.c | 2 +- arch/x86/kernel/cpu/intel.c | 152 +++++++++++++++--- arch/x86/kernel/traps.c | 7 + include/linux/sched/user.h | 4 +- kernel/user.c | 7 + 10 files changed, 182 insertions(+), 32 deletions(-) -- 2.29.2