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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1F6F9C33CA9 for ; Mon, 13 Jan 2020 19:05:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 003A521556 for ; Mon, 13 Jan 2020 19:05:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728669AbgAMTFg (ORCPT ); Mon, 13 Jan 2020 14:05:36 -0500 Received: from mx01.bbu.dsd.mx.bitdefender.com ([91.199.104.161]:35650 "EHLO mx01.bbu.dsd.mx.bitdefender.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726435AbgAMTFg (ORCPT ); Mon, 13 Jan 2020 14:05:36 -0500 X-Greylist: delayed 614 seconds by postgrey-1.27 at vger.kernel.org; Mon, 13 Jan 2020 14:05:34 EST Received: from smtp.bitdefender.com (smtp02.buh.bitdefender.net [10.17.80.76]) by mx01.bbu.dsd.mx.bitdefender.com (Postfix) with ESMTPS id 9B93A30747C7; Mon, 13 Jan 2020 20:55:19 +0200 (EET) Received: from localhost (unknown [195.210.5.22]) by smtp.bitdefender.com (Postfix) with ESMTPSA id 8A256301B92B; Mon, 13 Jan 2020 20:55:19 +0200 (EET) From: Adalbert =?iso-8859-2?b?TGF643I=?= Subject: Re: [RESEND PATCH v10 06/10] vmx: spp: Set up SPP paging table at vmentry/vmexit To: Sean Christopherson , Yang Weijiang Cc: 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 In-Reply-To: <20200113173358.GC1175@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> Date: Mon, 13 Jan 2020 20:55:46 +0200 Message-ID: <15789417460.A97E650.22893@host> User-agent: void Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Archived-At: List-Archive: List-Post: 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. https://lore.kernel.org/kvm/20190809160047.8319-62-alazar@bitdefender.com/