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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 7FE87C432C0 for ; Fri, 22 Nov 2019 01:52:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 501D02067D for ; Fri, 22 Nov 2019 01:52:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726532AbfKVBw1 (ORCPT ); Thu, 21 Nov 2019 20:52:27 -0500 Received: from mga07.intel.com ([134.134.136.100]:61190 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726265AbfKVBw1 (ORCPT ); Thu, 21 Nov 2019 20:52:27 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Nov 2019 17:52:26 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,228,1571727600"; d="scan'208";a="205263047" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by fmsmga008.fm.intel.com with ESMTP; 21 Nov 2019 17:52:25 -0800 Date: Thu, 21 Nov 2019 17:52:25 -0800 From: Sean Christopherson To: Fenghua Yu Cc: Andy Lutomirski , Xiaoyao Li , "Luck, Tony" , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin , "Raj, Ashok" , "Shankar, Ravi V" , linux-kernel , x86 Subject: Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter Message-ID: <20191122015225.GG16617@linux.intel.com> References: <3908561D78D1C84285E8C5FCA982C28F7F4DC167@ORSMSX115.amr.corp.intel.com> <20191121235329.GE199273@romley-ivt3.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191121235329.GE199273@romley-ivt3.sc.intel.com> 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 Thu, Nov 21, 2019 at 03:53:29PM -0800, Fenghua Yu wrote: > On Thu, Nov 21, 2019 at 03:18:46PM -0800, Andy Lutomirski wrote: > > > > > On Nov 21, 2019, at 2:29 PM, Luck, Tony wrote: > > > > > >> It would be really, really nice if we could pass this feature through to a VM. Can we? > > > > > > It's hard because the MSR is core scoped rather than thread scoped. So on an HT > > > enabled system a pair of logical processors gets enabled/disabled together. > > > > > > > Well that sucks. > > > > Could we pass it through if the host has no HT? Debugging is *so* much > > easier in a VM. And HT is a bit dubious these days anyway. > > I think it's doable to pass it through to KVM. The difficulty is to disable > split lock detection in KVM because that will disable split lock on the whole > core including threads for the host. Without disabling split lock in KVM, > it's doable to debug split lock in KVM. > > Sean and Xiaoyao are working on split lock for KVM (in separate patch set). > They may have insight on how to do this. Yes, with SMT off KVM could allow the guest to enable split lock #AC, but for the initial implementation we'd want to allow it if and only if split lock #AC is disabled in the host kernel. Otherwise we have to pull in the logic to control whether or not a guest can disable split lock #AC, what to do if a split lock #AC happens when it's enabled by the host but disabled by the guest, etc...