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 06056C33C9E for ; Tue, 14 Jan 2020 18:58:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DE4772467C for ; Tue, 14 Jan 2020 18:58:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728787AbgANS6J (ORCPT ); Tue, 14 Jan 2020 13:58:09 -0500 Received: from mga04.intel.com ([192.55.52.120]:30876 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726053AbgANS6J (ORCPT ); Tue, 14 Jan 2020 13:58:09 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Jan 2020 10:58:08 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,319,1574150400"; d="scan'208";a="249500514" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by fmsmga001.fm.intel.com with ESMTP; 14 Jan 2020 10:58:08 -0800 Date: Tue, 14 Jan 2020 10:58:08 -0800 From: Sean Christopherson To: Yang Weijiang Cc: 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: <20200114185808.GI16784@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> <20200114030820.GA4583@local-michael-cet-test.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200114030820.GA4583@local-michael-cet-test.sh.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 Tue, Jan 14, 2020 at 11:08:20AM +0800, Yang Weijiang wrote: > 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 I'm confused. It sounds like KVM_EXIT_SPP provides the instruction length because it skips an instruction before exiting to userspace. But if KVM is is emulating an instruction, it shouldn't be doing {kvm_}skip_emulated_instruction(), e.g. if emulation fails due to a SPP violation (returns KVM_EXIT_SPP) then GUEST_RIP should still point at the exiting instruction. Ditto for the fast_page_fault() case, RIP shouldn't be advanced. What am I missing? > 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? I'm not convinced the instruction length needs to be provided to userspace for this case. Obviously it's not difficult to provide the info, I just don't understand the value added by doing so. As above, RIP shouldn't need to be unwound, and blindly skipping an instruction seems like an odd thing for a VMI engine to do. > > 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. Can we make SPP dependent on unrestricted guest so that the only entry point to the emulator is through handle_ept_violation()? And thus the only path to triggering KVM_EXIT_SPP would also be through handle_ept_violation(); (I think, might be forgetting a different emulation path). > > > 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?