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=-10.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 27538C432BE for ; Fri, 6 Aug 2021 11:58:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 05F6561102 for ; Fri, 6 Aug 2021 11:58:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245668AbhHFL6W (ORCPT ); Fri, 6 Aug 2021 07:58:22 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:52461 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230373AbhHFL6U (ORCPT ); Fri, 6 Aug 2021 07:58:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628251084; 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=WsFUm2Fex09UP/JQJ5oBYUs9L6S3a0XW+Bgd7Je/qd4=; b=jACuhYfxkKpvtW1oBoy4GeWbeXBO++3To//qIz6KlPgn2sw9qnd2qolnAo2KmvpV5gm+h+ iP6tHmGBRKbM5Rg2lyoKustnGQqrqiis4IQnBh92DpYHN03fkiqCQtxZkjkY8teN7ZhV8q lj+AonJYEkF4b/yWwDSd5lZ+CEl+bf8= Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-452-ULLuJHCqOumihPoL332QdQ-1; Fri, 06 Aug 2021 07:58:03 -0400 X-MC-Unique: ULLuJHCqOumihPoL332QdQ-1 Received: by mail-ed1-f69.google.com with SMTP id dn10-20020a05640222eab02903bd023ea9f6so4776078edb.14 for ; Fri, 06 Aug 2021 04:58:03 -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=WsFUm2Fex09UP/JQJ5oBYUs9L6S3a0XW+Bgd7Je/qd4=; b=OryVfBfI9XiPcP/ZgxXk+JFGuSEflfgnDUHZvQwzZmKwOzmT2rm+7Fz5/BcfhPgWUl B8EcxCYqSMA28ZYlqv5EgHGLsyyfcIPRwu/rBO6/m46DwvFteypaBKWwM7rxCTS3LRQF 9b+aSkOkjXzXjptM0sRX7JC9spC/KDBfKOUutegTum2nmU9U9VgBAbq9fZ+7iL1HgTL6 WlJZxBEks/RLM1ERP3r1i0BJfNFU0cgzCH8xz82ZFS1VmGd+g1P5dzLzzyp3P4xZgvnL pKvhleEVftJYiYYBJxAJJGeeW+0Ojib+qINXz+hjRXvX3KEeM/b6YSd1Jsx4a8j3r/V3 Twhw== X-Gm-Message-State: AOAM5322n7PoYlpiA6zH1bYAT/iIn1ml5BcmOVHwv1OmUT3k1su8qRCk dzVFTg//52fB3e05ikQlRiiec8cEQ8+oq8vjDwYOppsOgEWQST77qL9y9jsHVah/sB7vpamOy2D gbJHo6ozkJ/9ygJIuhoLUWmM/W++wiP9PHzkK/cg3DzUrhKNmQgOxOmSZ57kFHK7YBC6Up5wXdG iX X-Received: by 2002:a17:907:2595:: with SMTP id ad21mr9166371ejc.430.1628251082398; Fri, 06 Aug 2021 04:58:02 -0700 (PDT) X-Google-Smtp-Source: ABdhPJylY//hOXD/73qc587D65K41qOTA088fVA2wMV+LUzQVJR46b1Vn56ScUwZQ9Yhu1huHNyzmA== X-Received: by 2002:a17:907:2595:: with SMTP id ad21mr9166352ejc.430.1628251082174; Fri, 06 Aug 2021 04:58:02 -0700 (PDT) Received: from ?IPv6:2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e? ([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id w23sm3708888edx.34.2021.08.06.04.58.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Aug 2021 04:58:01 -0700 (PDT) Subject: Re: [PATCH] KVM: x86: Allow guest to set EFER.NX=1 on non-PAE 32-bit kernels To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210805183804.1221554-1-seanjc@google.com> From: Paolo Bonzini Message-ID: Date: Fri, 6 Aug 2021 13:58:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210805183804.1221554-1-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 05/08/21 20:38, Sean Christopherson wrote: > Fast forward to today, and KVM has long since stopped running the guest > with the host's EFER.NX. Not only does KVM context switch EFER if > host.EFER.NX=1 && guest.EFER.NX=0, KVM also forces host.EFER.NX=0 && > guest.EFER.NX=1 when using shadow paging (to emulate SMEP). Furthermore, > the entire motivation for the restriction was made obsolete over a decade > ago when Intel added dedicated host and guest EFER fields in the VMCS > (Nehalem timeframe), which reduced the overhead of context switching EFER > from 400+ cycles (2 * WRMSR + 1 * RDMSR) to a mere ~2 cycles. Both pretty good points. :) Queued, thanks. Paolo