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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7F40C678D5 for ; Mon, 9 Jan 2023 16:30:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234855AbjAIQ37 (ORCPT ); Mon, 9 Jan 2023 11:29:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58516 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234895AbjAIQ3c (ORCPT ); Mon, 9 Jan 2023 11:29:32 -0500 Received: from mail-pf1-x42e.google.com (mail-pf1-x42e.google.com [IPv6:2607:f8b0:4864:20::42e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 13C4212614 for ; Mon, 9 Jan 2023 08:29:31 -0800 (PST) Received: by mail-pf1-x42e.google.com with SMTP id 20so1130634pfu.13 for ; Mon, 09 Jan 2023 08:29:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=35yBMGVdrFXKJkciDZqNeFdzTTlTrzLnN/meJzr1Na4=; b=FdnVV2CbXLr1oFYsEnHGPjy6OncknXV1I0BYvVhPA5iHGxxn/5AiETTfumk7M3CILn kYpCXoBmKqBr7RDhs6heKYOmT26XRzgn4PozrZlwT2RvlGrHhSUrZs83uBbKlRHcwY2x ISknDgemm8HojoWvfSK+DcztipGnfggfkrvxNIfQV6tq/+SqhSNIoXqRzAR8iBBhsKAH eg1m7dyveet1BUMz62yKQH5dSo/AhccPLrNUcBviEtFOeFBXUaZHXykrrcKuuE63v2HD BCaa1HqOma/K5Y3yVLMbmDbc42o8puDPzw91daIPue5lkUYbbZ/Ec0SJZe8j4sJkVXtZ xYmQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=35yBMGVdrFXKJkciDZqNeFdzTTlTrzLnN/meJzr1Na4=; b=8AHl7NbhNDbPN6Tp651g6RPBEwwl2gYGkV/TAH4vPZGdKQCskj5TR2wVoe3bDfCOS6 4Ky/6geHdwmsVAJrzvWjIgZHzFLYuJrllNPFeJ4dLBestlhZNvwToG8rEiklribnsMZp ZMeYg3edXnM2kiHIhwiOE3tWkJOBWp1qwuQmq2K+Vz9Xu2O5fs7zlRb71O4VLIM2bSNl Hda8Wb+rqLkX1pS0JNR6GUtdhb+fXEX/gFPwmZZ+CX6hYeczt3ZNPLJJdPsCgsXwivgD sICRC5LB9qrjXHEykpLPT3GHk+n6Ti8lJMo720+Pu7UspXmKLg1xlzfNCfokjLxr4YFk DBng== X-Gm-Message-State: AFqh2krPz7ZcOj+PWF7hU/8nFMhGIuoHBoTUb9EJ0ytXUh6TZTjik7FZ gNqeQC5fX6AtIrkygBLHEN/TVQ== X-Google-Smtp-Source: AMrXdXvs71bxrjRTj5qKxI0ejL6iobfb7xUEeYO5jYTm2rXDHtnDmUyWO1bs5r2cWRKM3abcEUUt9g== X-Received: by 2002:a05:6a00:1948:b0:581:bfac:7a52 with SMTP id s8-20020a056a00194800b00581bfac7a52mr657632pfk.1.1673281771259; Mon, 09 Jan 2023 08:29:31 -0800 (PST) Received: from google.com (7.104.168.34.bc.googleusercontent.com. [34.168.104.7]) by smtp.gmail.com with ESMTPSA id y22-20020aa78f36000000b00562677968aesm6265168pfr.72.2023.01.09.08.29.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Jan 2023 08:29:30 -0800 (PST) Date: Mon, 9 Jan 2023 16:29:27 +0000 From: Sean Christopherson To: Robert Hoo Cc: pbonzini@redhat.com, kirill.shutemov@linux.intel.com, kvm@vger.kernel.org, Jingqi Liu Subject: Re: [PATCH v3 2/9] KVM: x86: Add CR4.LAM_SUP in guest owned bits Message-ID: References: <20221209044557.1496580-1-robert.hu@linux.intel.com> <20221209044557.1496580-3-robert.hu@linux.intel.com> <5f2f0a44fbb1a2eab36183dfc2fcaf53e1109793.camel@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5f2f0a44fbb1a2eab36183dfc2fcaf53e1109793.camel@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Sat, Jan 07, 2023, Robert Hoo wrote: > On Sat, 2023-01-07 at 00:38 +0000, Sean Christopherson wrote: > > On Fri, Dec 09, 2022, Robert Hoo wrote: > > > If LAM enabled, CR4.LAM_SUP is owned by guest; otherwise, reserved. > > > > Why is it passed through to the guest? > > I think no need to intercept guest's control over CR4.LAM_SUP, which > controls LAM appliance to supervisor mode address. That's not a sufficient justification. KVM doesn't strictly need to intercept most CR4 bits, but not intercepting has performance implications, e.g. KVM needs to do a VMREAD(GUEST_CR4) to get LAM_SUP if the bit is pass through. As a base rule, KVM intercepts CR4 bits unless there's a reason not to, e.g. if the CR4 bit in question is written frequently by real guests and/or never consumed by KVM.