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=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 6B412C433F5 for ; Tue, 14 Sep 2021 11:39:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5105460F4A for ; Tue, 14 Sep 2021 11:39:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232426AbhINLk6 (ORCPT ); Tue, 14 Sep 2021 07:40:58 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:57605 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232418AbhINLkx (ORCPT ); Tue, 14 Sep 2021 07:40:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631619575; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VXsGLVph1NbqQ2nkvDoWH9B2JiDcc6lqU3jEfo1REJk=; b=SWLmyt/kaSxpj4MLSWPnV9hKO8tEBoiocDkndHhrqdufWdoI+3xW0YmSR242T8d3e0O9Rh 2Xbr/h2kBNAuWN6dABimbyur9/WxHRyblAu2Q6s2tS47K7v3OeUxwtVKGrw3GLZrmJyH9h B2aVJ+HLAbhTIJ6imDM18qouvZRQWU0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-456-WrrSKas9MgCaVgh6GAv1lQ-1; Tue, 14 Sep 2021 07:39:32 -0400 X-MC-Unique: WrrSKas9MgCaVgh6GAv1lQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 498B71811EC1; Tue, 14 Sep 2021 11:39:30 +0000 (UTC) Received: from starship (unknown [10.35.206.50]) by smtp.corp.redhat.com (Postfix) with ESMTP id 16CA81002388; Tue, 14 Sep 2021 11:39:24 +0000 (UTC) Message-ID: <5fec07dfcfd53421293c3814796f1aa4add4a126.camel@redhat.com> Subject: Re: [RFC PATCH 3/3] nSVM: use svm->nested.save to load vmcb12 registers and avoid TOC/TOU races From: Maxim Levitsky To: Emanuele Giuseppe Esposito , kvm@vger.kernel.org Cc: Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org Date: Tue, 14 Sep 2021 14:39:23 +0300 In-Reply-To: References: <20210903102039.55422-1-eesposit@redhat.com> <20210903102039.55422-4-eesposit@redhat.com> <21d2bf8c4e3eb3fc5d297fd13300557ec686b625.camel@redhat.com> <73b5a5bb-48f2-3a08-c76b-a82b5b69c406@redhat.com> <9585f1387b2581d30b74cd163a9aac2adbd37a93.camel@redhat.com> <2b1e17416cef1e37f42e9bc8b2283b03d2651cb2.camel@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2021-09-14 at 12:52 +0200, Emanuele Giuseppe Esposito wrote: > > I would do it this way: > > > > struct svm_nested_state { > > ... > > /* cached fields from the vmcb12 */ > > struct vmcb_control_area_cached ctl; > > struct vmcb_save_area_cached save; > > ... > > }; > > > > > > The only thing that requires a little bit of additional work when > applying this is svm_get_nested_state() (and theoretically > svm_set_nested_state(), in option 2). In this function, nested.ctl is > copied in user_vmcb->control. But now nested.ctl is not anymore a > vmcb_control_area, so the sizes differ. > > There are 2 options here: > 1) copy nested.ctl into a full vmcb_control_area, and copy it to user > space without modifying the API. The advantage is that the API is left > intact, but an additional copy is required. Thankfully there KVM_GET_NESTED_STATE is not performance critical at all, so a copy isn't that big problem, other that it is a bit ugly. Ugh.. > > 2) modify KVM_GET_NESTED_STATE and KVM_SET_NESTED_STATE to handle > vmcb_control_area_cached. Advantage is that there is a lightweight copy > + the benefits explained by you in the previous email (no unset field). That would break the KVM_GET_NESTED_STATE ABI without a very good reason, especially since some of the currently unused fields in the ctl (there are I think very few of them), might became used later on, needing to break the ABI again. Best regards, Maxim Levitsky > > I am not sure which one is the preferred way here. > > Thank you, > Emanuele >