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 5D80CC2D0DB for ; Thu, 23 Jan 2020 16:16:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2FDE02071E for ; Thu, 23 Jan 2020 16:16:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="FTBX6Mgg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728842AbgAWQQP (ORCPT ); Thu, 23 Jan 2020 11:16:15 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:27146 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726605AbgAWQQP (ORCPT ); Thu, 23 Jan 2020 11:16:15 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579796173; 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=EIV/YyjsNHKvzfLLRkCsSAhXa/8ugLsBC1Uq238ttpo=; b=FTBX6Mgggjswr7tcR6NC3OKAuxF4g1fgj1vD3uKHwU8F/plG4bX8xBB12YJIEWGYXL7gJp oEqYtlmnSOkZ1eW2u339EYemj+Hs2ryGbO/FAD8cn/hkSdnlxEeT2KS7raTxVqhufR9b2i y7T2MsIwntFy/ojnpY+e64OY0DBf6pw= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-302-22RGiMdpMsO3OeeOSU5W-w-1; Thu, 23 Jan 2020 11:16:08 -0500 X-MC-Unique: 22RGiMdpMsO3OeeOSU5W-w-1 Received: by mail-wr1-f69.google.com with SMTP id t3so2002290wrm.23 for ; Thu, 23 Jan 2020 08:16:08 -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=EIV/YyjsNHKvzfLLRkCsSAhXa/8ugLsBC1Uq238ttpo=; b=nhyGE1U9eYmVjjGaM39q/sLiEF9cCir3p8H/RawuQ5Y5cynsvCFPwz9jquHmYmAnsk yqNi1hSYIBSYKIXrrctB9xaSFl/VFMgBmyuuQ5+S7Kq9gzEgwpcSgFRobIimjhR+MNZ5 EifTDel3SZCem0zUdjsQD+R53tZ4mVRq53cpGrffYyUhBrgLUNeeYg238rQ7lzLylU9t uSlDu+9N29fmmpVzmiG2dyWTxvdlBApnJhKd23TqyoZJ6WmFgKYkJsGryEII8nNCLnNa LwTo9pfb2XtQWkoK7JR+Rnh/d86efbCWNMmZQYszaBP3rb/vtUEMoNqw8BPxTi5USshu CI2A== X-Gm-Message-State: APjAAAUCEEVr5CNDDIXcqpa8NTWBTogYgM40/BkrrGofcruiP7jZwKJ7 Zq079COOeQIqDVF7pTlhHMYpDVpzwoZRlT3ZCi+V2bBW874E4BZBzxIKPUq3OQiRXZVmMoDQZOi ANPr/Bi8EJFgcELT21Ea+Mr2R X-Received: by 2002:a7b:c3d8:: with SMTP id t24mr4902873wmj.175.1579796167373; Thu, 23 Jan 2020 08:16:07 -0800 (PST) X-Google-Smtp-Source: APXvYqzVie/mIIlbsyC2TD4OU1SdHGQkoaSGWQtEsx5eV8zH3zTTSAH+2bwHeH80HjHcBrDABuEkxw== X-Received: by 2002:a7b:c3d8:: with SMTP id t24mr4902864wmj.175.1579796167187; Thu, 23 Jan 2020 08:16:07 -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 w19sm3056765wmc.22.2020.01.23.08.16.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Jan 2020 08:16:06 -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: Date: Thu, 23 Jan 2020 17:16:06 +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? Just laziness I guess. Paolo