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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 AA533C3F2D1 for ; Thu, 5 Mar 2020 16:23:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8425C20848 for ; Thu, 5 Mar 2020 16:23:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726751AbgCEQXN (ORCPT ); Thu, 5 Mar 2020 11:23:13 -0500 Received: from mga02.intel.com ([134.134.136.20]:44356 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725938AbgCEQXN (ORCPT ); Thu, 5 Mar 2020 11:23:13 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 05 Mar 2020 08:23:11 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,518,1574150400"; d="scan'208";a="264022562" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by fmsmga004.fm.intel.com with ESMTP; 05 Mar 2020 08:23:11 -0800 Date: Thu, 5 Mar 2020 08:23:11 -0800 From: Sean Christopherson To: Xiaoyao Li Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , hpa@zytor.com, Paolo Bonzini , Andy Lutomirski , tony.luck@intel.com, peterz@infradead.org, fenghua.yu@intel.com, x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 2/8] x86/split_lock: Ensure X86_FEATURE_SPLIT_LOCK_DETECT means the existence of feature Message-ID: <20200305162311.GG11500@linux.intel.com> References: <20200206070412.17400-1-xiaoyao.li@intel.com> <20200206070412.17400-3-xiaoyao.li@intel.com> <20200303185524.GQ1439@linux.intel.com> <20200303194134.GW1439@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 04, 2020 at 09:49:14AM +0800, Xiaoyao Li wrote: > On 3/4/2020 3:41 AM, Sean Christopherson wrote: > >On Tue, Mar 03, 2020 at 10:55:24AM -0800, Sean Christopherson wrote: > >>On Thu, Feb 06, 2020 at 03:04:06PM +0800, Xiaoyao Li wrote: > >>>When flag X86_FEATURE_SPLIT_LOCK_DETECT is set, it should ensure the > >>>existence of MSR_TEST_CTRL and MSR_TEST_CTRL.SPLIT_LOCK_DETECT bit. > >> > >>The changelog confused me a bit. "When flag X86_FEATURE_SPLIT_LOCK_DETECT > >>is set" makes it sound like the logic is being applied after the feature > >>bit is set. Maybe something like: > >> > >>``` > >>Verify MSR_TEST_CTRL.SPLIT_LOCK_DETECT can be toggled via WRMSR prior to > >>setting the SPLIT_LOCK_DETECT feature bit so that runtime consumers, > >>e.g. KVM, don't need to worry about WRMSR failure. > >>``` > >> > >>>Signed-off-by: Xiaoyao Li > >>>--- > >>> arch/x86/kernel/cpu/intel.c | 41 +++++++++++++++++++++---------------- > >>> 1 file changed, 23 insertions(+), 18 deletions(-) > >>> > >>>diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c > >>>index 2b3874a96bd4..49535ed81c22 100644 > >>>--- a/arch/x86/kernel/cpu/intel.c > >>>+++ b/arch/x86/kernel/cpu/intel.c > >>>@@ -702,7 +702,8 @@ static void init_intel(struct cpuinfo_x86 *c) > >>> if (tsx_ctrl_state == TSX_CTRL_DISABLE) > >>> tsx_disable(); > >>>- split_lock_init(); > >>>+ if (boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT)) > >>>+ split_lock_init(); > >>> } > >>> #ifdef CONFIG_X86_32 > >>>@@ -986,9 +987,26 @@ static inline bool match_option(const char *arg, int arglen, const char *opt) > >>> static void __init split_lock_setup(void) > >>> { > >>>+ u64 test_ctrl_val; > >>> char arg[20]; > >>> int i, ret; > >>>+ /* > >>>+ * Use the "safe" versions of rdmsr/wrmsr here to ensure MSR_TEST_CTRL > >>>+ * and MSR_TEST_CTRL.SPLIT_LOCK_DETECT bit do exist. Because there may > >>>+ * be glitches in virtualization that leave a guest with an incorrect > >>>+ * view of real h/w capabilities. > >>>+ */ > >>>+ if (rdmsrl_safe(MSR_TEST_CTRL, &test_ctrl_val)) > >>>+ return; > >>>+ > >>>+ if (wrmsrl_safe(MSR_TEST_CTRL, > >>>+ test_ctrl_val | MSR_TEST_CTRL_SPLIT_LOCK_DETECT)) > >>>+ return; > >>>+ > >>>+ if (wrmsrl_safe(MSR_TEST_CTRL, test_ctrl_val)) > >>>+ return;a > >> > >>Probing the MSR should be skipped if SLD is disabled in sld_options, i.e. > >>move this code (and setup_force_cpu_cap() etc...) down below the > >>match_option() logic. The above would temporarily enable SLD even if the > >>admin has explicitly disabled it, e.g. makes the kernel param useless for > >>turning off the feature due to bugs. > > > >Hmm, but this prevents KVM from exposing SLD to a guest when it's off in > >the kernel, which would be a useful debug/testing scenario. > > > >Maybe add another SLD state to forcefully disable SLD? That way the admin > >can turn of SLD in the host kernel but still allow KVM to expose it to its > >guests. E.g. > > I don't think we need do this. > > IMO, this a the bug of split_lock_init(), which assume the initial value of > MSR_TEST_CTRL is zero, at least bit SPLIT_LOCK of which is zero. > This is problem, it's possible that BIOS has set this bit. Hmm, yeah, that's a bug. But it's a separate bug. > split_lock_setup() here, is to check if the feature really exists. So > probing MSR_TEST_CTRL and bit MSR_TEST_CTRL_SPLIT_LOCK_DETECT here. If there > all exist, setup_force_cpu_cap(X86_FEATURE_SPLIT_LOCK_DETECT) to indicate > feature does exist. > Only when feature exists, there is a need to parse the command line config > of split_lock_detect. Toggling SPLIT_LOCK before checking the kernel param is bad behavior, e.g. if someone has broken silicon that causes explosions if SPLIT_LOCK=1. The behavior is especially bad because cpu_set_core_cap_bits() enumerates split lock detection using FMS, i.e. clearcpuid to kill CORE_CAPABILITIES wouldn't work either.