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=-18.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 DB7C8C433E0 for ; Fri, 29 Jan 2021 17:01:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A9EF160234 for ; Fri, 29 Jan 2021 17:01:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231758AbhA2RAg (ORCPT ); Fri, 29 Jan 2021 12:00:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44716 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231774AbhA2Q7G (ORCPT ); Fri, 29 Jan 2021 11:59:06 -0500 Received: from mail-pl1-x62b.google.com (mail-pl1-x62b.google.com [IPv6:2607:f8b0:4864:20::62b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 42F0EC06174A for ; Fri, 29 Jan 2021 08:58:21 -0800 (PST) Received: by mail-pl1-x62b.google.com with SMTP id g3so5545160plp.2 for ; Fri, 29 Jan 2021 08:58:21 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=IEk9NbNMjO7h5rflP6rNtXSfouXuSq8Q4eNt49nSuwY=; b=F63YQDk3Poqo6G7huaqoQ1fSvxyg6l5KbYQ4I5whx29cPIni2xT+DzwDNiZxaXwICb tQRzSEsRG7ztZBQ3UExv4RsQvhP1fvEwURpOzQ4x81YJJADzXfELluRsX2NvlZhMEETR w5oyPLRXzAbrmL/6vBmXF9G9/tuI3gi7hUziAmaspvA+1wPcoknbl5R9EbxJuZedIzcB NuPYn6Qxa0x7njvsk3/nmtq9Kgnzr2bHN73HbeFRh7sv38UnG9WkZlIMZEc+FpuYtA8j pBKQhw2XzVSyPtd3I+PDSgWzHQotAg2q+/Pny7P/yWQl5MWVyLgYt8yHgjwCho6zU0Lv IECg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=IEk9NbNMjO7h5rflP6rNtXSfouXuSq8Q4eNt49nSuwY=; b=HkDk323vqUfBJ6DVAslLyhhLgKsRGs5HjADpPzDkwud8GXFIRdMIhxArSOAd0VYlOK dOAPJyS9MEI0of9BMiN1YVHNimSzpNesnxW/gUS0Dvv1tfM6CXW3O2pOQVmnFbSptYHK uQD9U9IuSNSR382FtE+pJNy6AH1tsAPII78Gye6Ido0zmDRikliB6BYudB8FRPdnrJmA F3LHz8izjWAxOvjV9u1hQDfR9pJHgr5OW2w3jL7clm9NAlHwUD+P4HPW+SkJDzzLc1VX upD5wzCSUiYW/lcDaGHJByt6TStWaGJBxmMQrWh9eKI/Nd/CDANdWq0e6yt90TAMMK24 YMCg== X-Gm-Message-State: AOAM531n4NaWGzzJ4LxHIg37kahQ4KZTxm1CyqOs/LngbdO3NmUfcFsg t8B7QSfxKR7yTenZwfvWg4hTQg== X-Google-Smtp-Source: ABdhPJwKYVSVJ9bIADbGcmcjCupj10IlJHIcWaq/HnZTkQL+2KhGaDFpDE1UFkyz6IEFkZVd3//Udg== X-Received: by 2002:a17:90a:448f:: with SMTP id t15mr5454936pjg.159.1611939500573; Fri, 29 Jan 2021 08:58:20 -0800 (PST) Received: from google.com ([2620:15c:f:10:91fd:c415:8a8b:ccc4]) by smtp.gmail.com with ESMTPSA id z18sm9447971pfj.102.2021.01.29.08.58.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 29 Jan 2021 08:58:19 -0800 (PST) Date: Fri, 29 Jan 2021 08:58:13 -0800 From: Sean Christopherson To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, jmattson@google.com, stable@vger.kernel.org Subject: Re: [PATCH v2] KVM: x86: Allow guests to see MSR_IA32_TSX_CTRL even if tsx=off Message-ID: References: <20210129101912.1857809-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210129101912.1857809-1-pbonzini@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 29, 2021, Paolo Bonzini wrote: > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 76bce832cade..15733013b266 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1401,7 +1401,7 @@ static u64 kvm_get_arch_capabilities(void) > * This lets the guest use VERW to clear CPU buffers. This comment be updated to call out the new TSX_CTRL behavior. /* * On TAA affected systems: * - nothing to do if TSX is disabled on the host. * - we emulate TSX_CTRL if present on the host. * This lets the guest use VERW to clear CPU buffers. */ > */ > if (!boot_cpu_has(X86_FEATURE_RTM)) > - data &= ~(ARCH_CAP_TAA_NO | ARCH_CAP_TSX_CTRL_MSR); > + data &= ~ARCH_CAP_TAA_NO; Hmm, simply clearing TSX_CTRL will only preserve the host value. Since ARCH_CAPABILITIES is unconditionally emulated by KVM, wouldn't it make sense to unconditionally expose TSX_CTRL as well, as opposed to exposing it only if it's supported in the host? I.e. allow migrating a TSX-disabled guest to a host without TSX. Or am I misunderstanding how TSX_CTRL is checked/used? > else if (!boot_cpu_has_bug(X86_BUG_TAA)) > data |= ARCH_CAP_TAA_NO; > > -- > 2.26.2 >