From patchwork Thu May 27 11:50:06 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Avi Kivity X-Patchwork-Id: 102614 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by demeter.kernel.org (8.14.3/8.14.3) with ESMTP id o4RBoTXT030443 for ; Thu, 27 May 2010 11:50:30 GMT Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934072Ab0E0LuU (ORCPT ); Thu, 27 May 2010 07:50:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34469 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759178Ab0E0LuM (ORCPT ); Thu, 27 May 2010 07:50:12 -0400 Received: from int-mx03.intmail.prod.int.phx2.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.16]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o4RBo8NZ017420 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Thu, 27 May 2010 07:50:08 -0400 Received: from cleopatra.tlv.redhat.com (cleopatra.tlv.redhat.com [10.35.255.11]) by int-mx03.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o4RBo7GM013924; Thu, 27 May 2010 07:50:07 -0400 Received: from file.tlv.redhat.com (file.tlv.redhat.com [10.35.255.8]) by cleopatra.tlv.redhat.com (Postfix) with ESMTP id 0353B250ADA; Thu, 27 May 2010 14:50:07 +0300 (IDT) From: Avi Kivity To: Xiao Guangrong , Marcelo Tosatti Cc: kvm@vger.kernel.org Subject: [PATCH 3/3] KVM: MMU: Document cr0.wp emulation Date: Thu, 27 May 2010 14:50:06 +0300 Message-Id: <1274961006-19413-4-git-send-email-avi@redhat.com> In-Reply-To: <1274961006-19413-1-git-send-email-avi@redhat.com> References: <1274961006-19413-1-git-send-email-avi@redhat.com> X-Scanned-By: MIMEDefang 2.67 on 10.5.11.16 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Greylist: IP, sender and recipient auto-whitelisted, not delayed by milter-greylist-4.2.3 (demeter.kernel.org [140.211.167.41]); Thu, 27 May 2010 11:50:30 +0000 (UTC) diff --git a/Documentation/kvm/mmu.txt b/Documentation/kvm/mmu.txt index 2201dcb..6528ad9 100644 --- a/Documentation/kvm/mmu.txt +++ b/Documentation/kvm/mmu.txt @@ -298,6 +298,24 @@ Host translation updates: - look up affected sptes through reverse map - drop (or update) translations +Emulating cr0.wp +================ + +If tdp is not enabled, the host must keep cr0.wp=1 so page write protection +works for the guest kernel, not guest guest userspace. When the guest +cr0.wp=1, this does not present a problem. However when the guest cr0.wp=0, +we cannot map the permissions for gpte.u=1, gpte.w=0 to any spte. + +We handle this my mapping the permissions to two possible gptes, depending +on fault type: + +- kernel write fault: spte.u=0, spte.w=1 (allows full kernel access, + disallows user access) +- read fault: spte.u=1, spte.w=0 (allows full read access, disallows kernel + write access) + +(user write faults generate a #PF) + Further reading ===============