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,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 ADFDCC33CA9 for ; Tue, 14 Jan 2020 03:03:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 89B8F2084D for ; Tue, 14 Jan 2020 03:03:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729420AbgANDDe (ORCPT ); Mon, 13 Jan 2020 22:03:34 -0500 Received: from mga07.intel.com ([134.134.136.100]:6662 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729325AbgANDDe (ORCPT ); Mon, 13 Jan 2020 22:03:34 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Jan 2020 19:03:33 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,431,1571727600"; d="scan'208";a="217601135" Received: from local-michael-cet-test.sh.intel.com (HELO localhost) ([10.239.159.128]) by orsmga008.jf.intel.com with ESMTP; 13 Jan 2020 19:03:32 -0800 Date: Tue, 14 Jan 2020 11:08:20 +0800 From: Yang Weijiang To: Sean Christopherson Cc: Yang Weijiang , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, jmattson@google.com, yu.c.zhang@linux.intel.com, alazar@bitdefender.com, edwin.zhai@intel.com Subject: Re: [RESEND PATCH v10 06/10] vmx: spp: Set up SPP paging table at vmentry/vmexit Message-ID: <20200114030820.GA4583@local-michael-cet-test.sh.intel.com> References: <20200102061319.10077-1-weijiang.yang@intel.com> <20200102061319.10077-7-weijiang.yang@intel.com> <20200110180458.GG21485@linux.intel.com> <20200113081050.GF12253@local-michael-cet-test.sh.intel.com> <20200113173358.GC1175@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200113173358.GC1175@linux.intel.com> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Jan 13, 2020 at 09:33:58AM -0800, Sean Christopherson wrote: > On Mon, Jan 13, 2020 at 04:10:50PM +0800, Yang Weijiang wrote: > > On Fri, Jan 10, 2020 at 10:04:59AM -0800, Sean Christopherson wrote: > > > On Thu, Jan 02, 2020 at 02:13:15PM +0800, Yang Weijiang wrote: > > > > @@ -3585,7 +3602,30 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level, > > > > if ((error_code & PFERR_WRITE_MASK) && > > > > spte_can_locklessly_be_made_writable(spte)) > > > > { > > > > - new_spte |= PT_WRITABLE_MASK; > > > > + /* > > > > + * Record write protect fault caused by > > > > + * Sub-page Protection, let VMI decide > > > > + * the next step. > > > > + */ > > > > + if (spte & PT_SPP_MASK) { > > > > + int len = kvm_x86_ops->get_inst_len(vcpu); > > > > > > There's got to be a better way to handle SPP exits than adding a helper > > > to retrieve the instruction length. > > > > > The fault instruction was skipped by kvm_skip_emulated_instruction() > > before, but Paolo suggested leave the re-do or skip option to user-space > > to make it flexible for write protection or write tracking, so return > > length to user-space. > > Sorry, my comment was unclear. I have no objection to punting the fault > to userspace, it's the mechanics of how it's done that I dislike. > > Specifically, (a) using run->exit_reason to propagate the SPP exit up the > stack, e.g. instead of modifying affected call stacks to play nice with > any exit to userspace, (b) assuming ->get_insn_len() will always be > accurate, e.g. see the various caveats in skip_emulated_instruction() for > both VMX and SVM, and (c) duplicating the state capture code in every > location that can encounter a SPP fault. How about calling skip_emulated_instruction() in KVM before exit to userspace, but still return the skipped instruction length, if userspace would like to re-execute the instruction, it can unwind RIP or simply rely on KVM? > > What I'm hoping is that it's possible to modify the call stacks to > explicitly propagate an exit to userspace and/or SPP fault, and shove all > the state capture into a common location, e.g. handle_ept_violation(). > The problem is, the state capture code in fast_page_fault() and emulation case share different causes, the former is generic occurence of SPP induced EPT violation, the latter is atually a "faked" one while detecting emulation instruction is writing some SPP protected area, so I seperated them. > Side topic, assuming the userspace VMI is going to be instrospecting the > faulting instruction, won't it decode the instruction? I.e. calculate > the instruction length anyways?