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 D2B0AC432C2 for ; Thu, 26 Sep 2019 09:26:04 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A1914217F4 for ; Thu, 26 Sep 2019 09:26:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A1914217F4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:32906 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iDQ2F-0000ze-2d for qemu-devel@archiver.kernel.org; Thu, 26 Sep 2019 05:26:03 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55747) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iDQ1G-0008TC-1X for qemu-devel@nongnu.org; Thu, 26 Sep 2019 05:25:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iDQ1C-0003tI-FS for qemu-devel@nongnu.org; Thu, 26 Sep 2019 05:25:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:8278) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iDQ1C-0003t6-9k for qemu-devel@nongnu.org; Thu, 26 Sep 2019 05:24:58 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 55EF230A7BB5; Thu, 26 Sep 2019 09:24:57 +0000 (UTC) Received: from maximlenovopc.usersys.redhat.com (unknown [10.35.206.33]) by smtp.corp.redhat.com (Postfix) with ESMTP id 07C6119C5B; Thu, 26 Sep 2019 09:24:55 +0000 (UTC) Message-ID: <7c019f3a5236daaa79e67467f64cde212ad05f35.camel@redhat.com> Subject: Re: Questions about the real mode in kvm/qemu From: Maxim Levitsky To: Paolo Bonzini , Li Qiang Date: Thu, 26 Sep 2019 12:24:55 +0300 In-Reply-To: <23789310-35fb-8c93-44f4-532bcd34007d@redhat.com> References: <644968ffb11c11fd580e96c1e67932501a633fe4.camel@redhat.com> <3d3f3a0e6e796260348c66e69e859e1901501ee8.camel@redhat.com> <23789310-35fb-8c93-44f4-532bcd34007d@redhat.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Thu, 26 Sep 2019 09:24:57 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Qemu Developers , Avi Kivity Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 2019-09-26 at 11:18 +0200, Paolo Bonzini wrote: > On 26/09/19 10:59, Maxim Levitsky wrote: > > If you mean to ask if there is a way to let guest access use no > > paging at all, that is access host physical addresses directly, then > > indeed there is no way, since regular non 'unrestricted guest' mode > > required both protected mode and paging, and 'unrestricted guest' > > requires EPT. Academically speaking it is of course possible to > > create paging tables that are 1:1... >=20 > Not so academically, it's exactly what KVM does. You mean KVM uses 1:1 EPT pages and no guest paging, to allow guest to access host physical address space? That would break the security completely, thus I think you mean something else here. > However, indeed it > would also be possible to switch out of EPT mode when CR0.PG=3D0. I'm = not > sure why it was done this way, maybe when the code was written it was > simpler to use the identity map. >=20 > Let's see if Avi is listening... :) >=20 > Paolo Here a quote from the PRM: "The first processors to support VMX operation require CR0.PE and CR0.PG = to be 1 in VMX operation (see Section 23.8). This restriction implies that guest software cannot be run in unpa= ged protected mode or in real-address mode. Later processors support a VM-execution control called =E2=80=9Cunr= estricted guest=E2=80=9D. 1 If this control is 1, CR0.PE and CR0.PG may be 0 in VMX non-root operation. Such processors allow guest so= ftware to run in unpaged protected mode or in real-address mode. The following items describe the behavior o= f such software:" ... "As noted in Section 26.2.1.1, the =E2=80=9Cenable EPT=E2=80=9D VM-execut= ion control must be 1 if the =E2=80=9Cunrestricted guest=E2=80=9D VM-exec= ution control is 1." Best regards, Maxim Levitsky