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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=unavailable 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 01F27C43460 for ; Wed, 7 Apr 2021 10:24:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AAEA861205 for ; Wed, 7 Apr 2021 10:24:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351068AbhDGKZD (ORCPT ); Wed, 7 Apr 2021 06:25:03 -0400 Received: from mx2.suse.de ([195.135.220.15]:42386 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351008AbhDGKYy (ORCPT ); Wed, 7 Apr 2021 06:24:54 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 28651B0B6; Wed, 7 Apr 2021 10:24:44 +0000 (UTC) Date: Wed, 7 Apr 2021 12:24:40 +0200 From: Borislav Petkov To: Christophe Leroy Cc: Sean Christopherson , Paolo Bonzini , Brijesh Singh , Tom Lendacky , John Allen , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 8/8] KVM: SVM: Allocate SEV command structures on local stack Message-ID: <20210407102440.GA25732@zn.tnic> References: <20210406224952.4177376-1-seanjc@google.com> <20210406224952.4177376-9-seanjc@google.com> <9df3b755-d71a-bfdf-8bee-f2cd2883ea2f@csgroup.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9df3b755-d71a-bfdf-8bee-f2cd2883ea2f@csgroup.eu> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org First of all, I'd strongly suggest you trim your emails when you reply - that would be much appreciated. On Wed, Apr 07, 2021 at 07:24:54AM +0200, Christophe Leroy wrote: > > @@ -258,7 +240,7 @@ static int sev_issue_cmd(struct kvm *kvm, int id, void *data, int *error) > > static int sev_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp) > > { > > struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info; > > - struct sev_data_launch_start *start; > > + struct sev_data_launch_start start; > > struct sev_data_launch_start start = {0, 0, 0, 0, 0, 0, 0}; I don't know how this is any better than using memset... Also, you can do ... start = { }; which is certainly the only other alternative to memset, AFAIK. But whatever you do, you need to look at the resulting asm the compiler generates. So let's do that: Your version: # arch/x86/kvm/svm/sev.c:261: struct sev_data_launch_start _tmp = {0, 0, 0, 0, 0, 0, 0}; movq $0, 104(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 112(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 120(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 128(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movl $0, 136(%rsp) #, MEM[(struct sev_data_launch_start *)_561] my version: # arch/x86/kvm/svm/sev.c:261: struct sev_data_launch_start _tmp = {}; movq $0, 104(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 112(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 120(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 128(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movl $0, 136(%rsp) #, MEM[(struct sev_data_launch_start *)_561] the memset version: # arch/x86/kvm/svm/sev.c:269: memset(&_tmp, 0, sizeof(_tmp)); #NO_APP movq $0, 104(%rsp) #, MEM [(void *)_561] movq $0, 112(%rsp) #, MEM [(void *)_561] movq $0, 120(%rsp) #, MEM [(void *)_561] movq $0, 128(%rsp) #, MEM [(void *)_561] movl $0, 136(%rsp) #, MEM [(void *)_561] Ok? -- Regards/Gruss, Boris. SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg