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 A27BEC33CA9 for ; Mon, 13 Jan 2020 21:47:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7DB9C20CC7 for ; Mon, 13 Jan 2020 21:47:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728842AbgAMVrO (ORCPT ); Mon, 13 Jan 2020 16:47:14 -0500 Received: from mga14.intel.com ([192.55.52.115]:27903 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726488AbgAMVrO (ORCPT ); Mon, 13 Jan 2020 16:47:14 -0500 X-Amp-Result: UNSCANNABLE 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; 13 Jan 2020 13:47:13 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,430,1571727600"; d="scan'208";a="217534645" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga008.jf.intel.com with ESMTP; 13 Jan 2020 13:47:13 -0800 Date: Mon, 13 Jan 2020 13:47:13 -0800 From: Sean Christopherson To: Adalbert =?utf-8?B?TGF6xINy?= Cc: Yang Weijiang , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, jmattson@google.com, yu.c.zhang@linux.intel.com, edwin.zhai@intel.com, tamas@tklengyel.com, mathieu.tarral@protonmail.com Subject: Re: [RESEND PATCH v10 06/10] vmx: spp: Set up SPP paging table at vmentry/vmexit Message-ID: <20200113214713.GG2322@linux.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> <15789417460.A97E650.22893@host> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <15789417460.A97E650.22893@host> 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 Mon, Jan 13, 2020 at 08:55:46PM +0200, Adalbert Lazăr wrote: > On Mon, 13 Jan 2020 09:33:58 -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. > > > > 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(). > > > > 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? > > Indeed, we decode the instruction from userspace. I don't know if the > instruction length helps other projects. Added Tamas and Mathieu. > > In our last VMI API proposal, the breakpoint event had the instruction > length sent to userspace, but I can't remember why. INT3 is trap-like, i.e. the VM-Exit occurs after the instruction retires. It's impossible for software to know how far to unwind RIP without the instruction length being provided by hardware/KVM, e.g. if the guest is being silly and prepends ignored prefixes on the INT3. Self-aware software has a priori knowledge of what's being patched in, and practically speaking I don't any well-behaved sane software uses prefixes with INT3, but from a VMM's perspective it's legal and possible. > > https://lore.kernel.org/kvm/20190809160047.8319-62-alazar@bitdefender.com/