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=-2.4 required=3.0 tests=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 906F8C2D0DB for ; Thu, 23 Jan 2020 16:16:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6349A21835 for ; Thu, 23 Jan 2020 16:16:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OgPUz7Lm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729074AbgAWQQ3 (ORCPT ); Thu, 23 Jan 2020 11:16:29 -0500 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:37895 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729009AbgAWQQ3 (ORCPT ); Thu, 23 Jan 2020 11:16:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579796188; 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=5sIIr88lSbFA0BlG1nNmj6Enx5IlWKEvDOlX33MYcGs=; b=OgPUz7LmUbGyz4fgdndoshzS2s2d6N4us8vnQsh3vRcHhV9t/iPw98bDJtsXQrDO11xrqA QybRvn1qZWWiyGpDsUfkamP4Hw0uCTa+AEnkuWJXwMC+L2tJNU1w6XGCEHRU5D3y8cnZ3H LluBH73yaxvF5vEoDQ7Ab8bX+wK9j/E= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-99-IjOkF_JHNOaY2oyOgRjHow-1; Thu, 23 Jan 2020 11:16:24 -0500 X-MC-Unique: IjOkF_JHNOaY2oyOgRjHow-1 Received: by mail-wm1-f69.google.com with SMTP id m21so729437wmg.6 for ; Thu, 23 Jan 2020 08:16:23 -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=5sIIr88lSbFA0BlG1nNmj6Enx5IlWKEvDOlX33MYcGs=; b=b8hFB7yd/VY34YSJH2gterawGT73pAxvxixe+IwbqNhzJtCwyqXcl5oG/m9v7gslL5 Rav/lhZoVYTF8LPU5pNlLjiA/4OrKFAJEU0J5SEmGOih8ofQex532PutSd8ijOR6Zn1v BI4OG0729NvgJ6FzpABf7IPwqYWjfevVeb83/rfSB9yclG3pLjhZ4VacpgEGaLV9ppXm FwX2lvCMMw4/zUyuqJ9iR8LLTH9RNmApn9n9dY0LhgoWbarrxieDKeqiE4YnG5gJNNWj RRZyOGOhUmKYkypTd/2d9+RX4AjKdMzkvH14AjiLHy9O+j+aZHNRVfKxh6y5BCdu7YpS v4sA== X-Gm-Message-State: APjAAAWrBn+CYVxMIvPLUVeFW3KICcFzsSp1u/gaInkxnD2c48RBnWsu AH3krvhS0n89JXzZ8a9xMQrxzds5QAgLi8PnZcEm1aZCY0ijl2xRKirmsU4d6zmLd2RUN1bOf+C Ql/BYqzC0gHdj46pWmewfHyp/ X-Received: by 2002:a1c:1b42:: with SMTP id b63mr2167997wmb.16.1579796182461; Thu, 23 Jan 2020 08:16:22 -0800 (PST) X-Google-Smtp-Source: APXvYqxSF26kJs+JPMSG10GEDEcJjNLaTdakZx0Dm0y+GVghiwYl96TqI7gbcuuqv9s25ojTDMfPCg== X-Received: by 2002:a1c:1b42:: with SMTP id b63mr2167981wmb.16.1579796182282; Thu, 23 Jan 2020 08:16:22 -0800 (PST) Received: from ?IPv6:2001:b07:6468:f312:b8fe:679e:87eb:c059? ([2001:b07:6468:f312:b8fe:679e:87eb:c059]) by smtp.gmail.com with ESMTPSA id a9sm3117714wmm.15.2020.01.23.08.16.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Jan 2020 08:16:21 -0800 (PST) Subject: Re: [RESEND] Atomic switch of MSR_IA32_UMWAIT_CONTROL To: Sean Christopherson , Tao Xu , Jingqi Liu Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200123154526.GC13178@linux.intel.com> From: Paolo Bonzini Message-ID: <0146cafa-9713-59a7-00b7-87add0ab0738@redhat.com> Date: Thu, 23 Jan 2020 17:16:21 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20200123154526.GC13178@linux.intel.com> Content-Type: text/plain; charset=windows-1252 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 23/01/20 16:45, Sean Christopherson wrote: > cc'ing KVM and LKML this time... > > Why does KVM use the atomic load/store lists to load MSR_IA32_UMWAIT_CONTROL > on VM-Enter/VM-Exit? Unless the host kernel is doing UWMAIT, which it > really shouldn't and AFAICT doesn't, isn't it better to use the shared MSR > mechanism to load the host value only when returning to userspace, and > reload the guest value on demand? > To clarify, laziness also on part of the reviewer, aka me. Paolo