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=-6.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 2EBBBC00A89 for ; Sat, 31 Oct 2020 00:27:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DF1E7206E5 for ; Sat, 31 Oct 2020 00:27:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725926AbgJaA1x (ORCPT ); Fri, 30 Oct 2020 20:27:53 -0400 Received: from mga06.intel.com ([134.134.136.31]:24067 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725446AbgJaA1x (ORCPT ); Fri, 30 Oct 2020 20:27:53 -0400 IronPort-SDR: m9/GxqAQraEtEekYzt+V6sb68YWpSJtzWr2qvFpQKNBALJRf8kTQ2QzNVql1WWb6TYwYJCMYFk S6Mv9hl+SXCQ== X-IronPort-AV: E=McAfee;i="6000,8403,9790"; a="230318023" X-IronPort-AV: E=Sophos;i="5.77,435,1596524400"; d="scan'208";a="230318023" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Oct 2020 17:27:53 -0700 IronPort-SDR: MQlrTZMYLXGOeRlKjMOe8kvXP6V7s+AUaJYIEoF0cDAgfKNVho4uRVnXjzicC8hJ+69Ow5snBy j+KJTo3cZGOg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.77,435,1596524400"; d="scan'208";a="469683903" Received: from otcwcpicx6.sc.intel.com ([172.25.55.29]) by orsmga004.jf.intel.com with ESMTP; 30 Oct 2020 17:27:52 -0700 From: Fenghua Yu To: "Thomas Gleixner" , "Borislav Petkov" , "Ingo Molnar" , "Peter Zijlstra" , "Randy Dunlap" , "Tony Luck" , "Christopherson Sean J" , "Ashok Raj" , "Ravi V Shankar" Cc: "linux-kernel" , "x86" , Fenghua Yu Subject: [PATCH RFC v3 0/4] x86/bus_lock: Enable bus lock detection Date: Sat, 31 Oct 2020 00:27:10 +0000 Message-Id: <20201031002714.3649728-1-fenghua.yu@intel.com> X-Mailer: git-send-email 2.29.1 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] Chapter 8 https://software.intel.com/sites/default/files/managed/c5/15/architecture-instruction-set-extensions-programming-reference.pdf Change Log: 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 | 28 +++- arch/x86/include/asm/cpu.h | 10 +- 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 | 145 +++++++++++++++--- arch/x86/kernel/traps.c | 7 + include/linux/sched/user.h | 4 +- kernel/user.c | 7 + 10 files changed, 176 insertions(+), 30 deletions(-) -- 2.29.1