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=-18.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 8E472C433E0 for ; Wed, 3 Feb 2021 08:04:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E4B164F4E for ; Wed, 3 Feb 2021 08:04:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232457AbhBCIE1 (ORCPT ); Wed, 3 Feb 2021 03:04:27 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:26079 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232332AbhBCIEX (ORCPT ); Wed, 3 Feb 2021 03:04:23 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612339376; 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=kEMHaMwbi3AuNVus+rKLM1JLdZEfgnKxlFjzFWyQHnE=; b=Pl58sM6qgmPB+8MBPSkaNtaVLbPU0xtvo/tipK9Td7B1HWfHLH+7OA2SNjEBfQ8gLoBrff 8s/AbS1JLNjbKwbny1OcR+ePkAcKZHoQ4GCwpsdZV0U1/LFVtofZ+Tt6m15Io5NwZXeezg AHMnimjCb43bkL596wk2VQZmNSmmrKw= Received: from mail-ej1-f69.google.com (mail-ej1-f69.google.com [209.85.218.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-228-GYcMkaJHPVej4sRN7hS0ag-1; Wed, 03 Feb 2021 03:02:55 -0500 X-MC-Unique: GYcMkaJHPVej4sRN7hS0ag-1 Received: by mail-ej1-f69.google.com with SMTP id hx26so5197644ejc.3 for ; Wed, 03 Feb 2021 00:02:55 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=kEMHaMwbi3AuNVus+rKLM1JLdZEfgnKxlFjzFWyQHnE=; b=BOoU6hII2mvBp373Zyj/HSWz8TvPAazzayZSzZSn3hQD6eY5pQ9Jvwk4R/6l38e0vT wER21OjzgZ8S08ePJUYZ+8H/l1loX6qtcya+QpwgrPimruB5aMrfmrnzXG+zDoWVVAP6 BgaqdekeKSm3lxdAzDqC1eev29roNAnkc7fjXR71r3lkGHfgsaV5F39McHJ8+DJ20X6e H3Wp4FcWJHgb5S+FnwZ+kwFRlMwmgUBoqL2BXh+Omi01rXyhpVjsthLZFN2tWAE0tP+p iSDLgN8Sbcmz0xjv1QaRXjR3vuaNSxn216+v4Dlxr6p38SgZn2NSVLJa+eq1qy1gTthn l+Lw== X-Gm-Message-State: AOAM533P6OHICx4KOMuezbY2+o3eZfiWIdSyLvjJceVdPyZu3FqotQXW dkkSbphVnOU0d8B8Vy6oKZhKZ84r0JBhWB3ncxqZYzX8o2j4ejgmopDGfNopzyfIaYFi0tJChpy P1Pi2r9rJr6/5dS1xHPr+NAyz6a9tq62CaDXf6b5AogkYHlsGSY7xdMIJZJqJB5gNWypFH7lVhI aK X-Received: by 2002:a17:907:2da0:: with SMTP id gt32mr1930614ejc.78.1612339373776; Wed, 03 Feb 2021 00:02:53 -0800 (PST) X-Google-Smtp-Source: ABdhPJwg8QEV5fFm0hkBGzPxCPlW5dNX5HELqVeWY3Alk0wm8qorBkOGSY6HZsOKSn9PPnLp7FCbIg== X-Received: by 2002:a17:907:2da0:: with SMTP id gt32mr1930589ejc.78.1612339373529; Wed, 03 Feb 2021 00:02:53 -0800 (PST) Received: from ?IPv6:2001:b07:6468:f312:c8dd:75d4:99ab:290a? ([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id l20sm607221ejb.95.2021.02.03.00.02.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 Feb 2021 00:02:52 -0800 (PST) Subject: Re: [PATCH] KVM: SVM: Treat SVM as unsupported when running as an SEV guest To: Sean Christopherson , Dave Hansen , Andy Lutomirski , Peter Zijlstra Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210202212017.2486595-1-seanjc@google.com> From: Paolo Bonzini Message-ID: <6b38551b-df22-7416-007c-d5f750940f9a@redhat.com> Date: Wed, 3 Feb 2021 09:02:51 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210202212017.2486595-1-seanjc@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/02/21 22:20, Sean Christopherson wrote: > Don't let KVM load when running as an SEV guest, regardless of what > CPUID says. Memory is encrypted with a key that is not accessible to > the host (L0), thus it's impossible for L0 to emulate SVM, e.g. it'll > see garbage when reading the VMCB. > > Technically, KVM could decrypt all memory that needs to be accessible to > the L0 and use shadow paging so that L0 does not need to shadow NPT, but > exposing such information to L0 largely defeats the purpose of running as > an SEV guest. This can always be revisited if someone comes up with a > use case for running VMs inside SEV guests. > > Note, VMLOAD, VMRUN, etc... will also #GP on GPAs with C-bit set, i.e. KVM > is doomed even if the SEV guest is debuggable and the hypervisor is willing > to decrypt the VMCB. This may or may not be fixed on CPUs that have the > SVME_ADDR_CHK fix. > > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson > --- > > FWIW, I did get nested SVM working on SEV by decrypting all structures > that are shadowed by L0, albeit with many restrictions. So even though > there's unlikely to be a legitimate use case, I don't think KVM (as L0) > needs to be changed to disallow nSVM for SEV guests, userspace is > ultimately the one that should hide SVM from L1. > > arch/x86/kvm/svm/svm.c | 5 +++++ > arch/x86/mm/mem_encrypt.c | 1 + > 2 files changed, 6 insertions(+) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index 687876211ebe..9fb367cb4f15 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -448,6 +448,11 @@ static int has_svm(void) > return 0; > } > > + if (sev_active()) { > + pr_info("KVM is unsupported when running as an SEV guest\n"); > + return 0; > + } > + > return 1; > } > > diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c > index c79e5736ab2b..c3d5f0236f35 100644 > --- a/arch/x86/mm/mem_encrypt.c > +++ b/arch/x86/mm/mem_encrypt.c > @@ -382,6 +382,7 @@ bool sev_active(void) > { > return sev_status & MSR_AMD64_SEV_ENABLED; > } > +EXPORT_SYMBOL_GPL(sev_active); > > /* Needs to be called from non-instrumentable code */ > bool noinstr sev_es_active(void) > Queued, thanks. Paolo