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=-5.4 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,USER_AGENT_SANE_1 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 274F7C433DF for ; Fri, 10 Jul 2020 17:40:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 01F732076A for ; Fri, 10 Jul 2020 17:40:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ijCxRGKx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728330AbgGJRkP (ORCPT ); Fri, 10 Jul 2020 13:40:15 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:41432 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727065AbgGJRkP (ORCPT ); Fri, 10 Jul 2020 13:40:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594402814; 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=/IkQPdXSHaUMhvBTo4/ZFo40yEF0ln1C5QCttyzLIBw=; b=ijCxRGKxqaOvCvELg3qGBYj5m07pSfSDlIxK6ax6CJcl87q51BEJRE/2VolWrpEpDaB31y cJOdUkamApe5IEkdgdQFntsK7X2ilEgIrXQSQ2Ill7jKMz55ETOnli1nvsx8vPP0QJZZeF X3MVsrvKG8vK9nJqCkZAX4XYFYe1PLg= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-58-yu7xFYdIMZat8vc-LrboQg-1; Fri, 10 Jul 2020 13:40:12 -0400 X-MC-Unique: yu7xFYdIMZat8vc-LrboQg-1 Received: by mail-wm1-f70.google.com with SMTP id 65so7400518wmd.8 for ; Fri, 10 Jul 2020 10:40:12 -0700 (PDT) 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=/IkQPdXSHaUMhvBTo4/ZFo40yEF0ln1C5QCttyzLIBw=; b=QmwwcVyUrmNGvcMPOa4Fv1AOYa6c3w/j5au5hQ9kpXQdm+tpeY7n4lTNqxFYvaLWkH exlxyNdao/8iakNgtt3FLa/pJMcEQA57gKLczsjWrluiEyWOMZY+Wnli6NLCEmKB6o9b 7J5mPpHOafBQstGJAcbFoD1xVdkoHvKHiF6F7BXI2x0Z5SGaNxbRKngdGNtdmb0G+ZGf 0XTw2YKes6zFmRL8+e+mNMRQyRC7nSZHbmkzyRb3ed3xEn5fdqB4kdj2zrGoE0ElZOUO 0eywZRDoMDp7snKXAU6cqzZF5FDI3yRjbhUKxfPnRgU5v0HtqXKCKZCCtjzB7ff0FuSM 4BmA== X-Gm-Message-State: AOAM533paZ/pZr9Jjp+hWeQifsqo4h8Z3M+f377nYQPgtBJGTICwljHK PRGzgoGUnxtbsgc0nx8n+GloA+Azd0+DrgpdyuZVsPNooJ5wZysN9ullfYrlzyVUYKB5wQooM7k aFApsIaxXw4rg3RMWis/ItX5O X-Received: by 2002:adf:f209:: with SMTP id p9mr65624120wro.86.1594402811225; Fri, 10 Jul 2020 10:40:11 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwgdBFsI6NpM0cOEYE9Zd0CxeHVbzpJqrUECEdskVqorMpkRotRA6xd/OKf7+5nsRvVTo8ujA== X-Received: by 2002:adf:f209:: with SMTP id p9mr65624106wro.86.1594402811022; Fri, 10 Jul 2020 10:40:11 -0700 (PDT) Received: from ?IPv6:2001:b07:6468:f312:9541:9439:cb0f:89c? ([2001:b07:6468:f312:9541:9439:cb0f:89c]) by smtp.gmail.com with ESMTPSA id c15sm10333052wme.23.2020.07.10.10.40.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Jul 2020 10:40:10 -0700 (PDT) Subject: Re: [PATCH v3 0/9] KVM: Support guest MAXPHYADDR < host MAXPHYADDR To: Jim Mattson Cc: Mohammed Gamal , kvm list , LKML , Vitaly Kuznetsov , Sean Christopherson , Wanpeng Li , Joerg Roedel References: <20200710154811.418214-1-mgamal@redhat.com> <0c892b1e-6fe6-2aa7-602e-f5fadc54c257@redhat.com> <9e784c62-15ee-63b7-4942-474493bac536@redhat.com> From: Paolo Bonzini Message-ID: <5d9e2483-81ba-1d94-5324-08245ced7d0e@redhat.com> Date: Fri, 10 Jul 2020 19:40:08 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/07/20 19:26, Jim Mattson wrote: >> Intel only has MAXPHYADDR > 46 on LA57 machines (because in general OSes >> like to have a physical 1:1 map into the kernel part of the virtual >> address space, so having a higher MAXPHYADDR would be of limited use >> with 48-bit linear addresses). > We all know that the direct map is evil. :-) > > Sorry it took me so long to get there. I didn't realize that Linux was > incapable of using more physical memory than it could map into the > kernel's virtual address space. (Wasn't that the whole point of PAE > originally?) Yes, but it's so slow that Linux preferred not to go that way for 64-bit kernels. That said, that justification for MAXPHYADDR==46 came from Intel processor architects, and when they say "OSes" they usually refer to a certain vendor from the Pacific north-west. Paolo