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=-7.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, HK_RANDOM_FROM,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,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 B8905C3F2D1 for ; Fri, 6 Mar 2020 02:15:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E72C2073D for ; Fri, 6 Mar 2020 02:15:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726846AbgCFCPc (ORCPT ); Thu, 5 Mar 2020 21:15:32 -0500 Received: from mga14.intel.com ([192.55.52.115]:62264 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726317AbgCFCPc (ORCPT ); Thu, 5 Mar 2020 21:15:32 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 05 Mar 2020 18:15:31 -0800 X-IronPort-AV: E=Sophos;i="5.70,520,1574150400"; d="scan'208";a="234638821" Received: from xiaoyaol-mobl.ccr.corp.intel.com (HELO [10.249.168.47]) ([10.249.168.47]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-SHA; 05 Mar 2020 18:15:26 -0800 Subject: Re: [PATCH v3 2/8] x86/split_lock: Ensure X86_FEATURE_SPLIT_LOCK_DETECT means the existence of feature To: Sean Christopherson 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 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> <20200305162311.GG11500@linux.intel.com> From: Xiaoyao Li Message-ID: <20bc0919-72ac-0445-29f2-2b445230faad@intel.com> Date: Fri, 6 Mar 2020 10:15:23 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200305162311.GG11500@linux.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/6/2020 12:23 AM, Sean Christopherson wrote: > 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. > It makes things complicated when we take all into account. We check kernel param first in BSP, if it's sld_off, we don't set flag X86_FEATURE_SPLIT_LOCK_DETECT. Of course during APs booting, there is no X86_FEATURE_SPLIT_LOCK_DETECT, it won't do split_lock_init(). However, due to X86_FEATURE_SPLIT_LOCK_DETECT flag not being set, clearing SLD bit in each AP when sld_off in case BIOS has set it, won't work. So in split_lock_setup() here, if sld_off, we don't set flag X86_FEATURE_SPLIT_LOCK_DETECT, and we also need to send IPI to each AP to clear SLD bit ?